Heathkit Darkroom timer revealed glory!

[Tin Can]

I bought a used Heathkit darkroom timer here. It was recently offered and the seller always sells great stuff. Look it up.

Heathkit holds a special place for some of us of a certain age. They made advanced electronic kits for skilled hobbyists.

I really regret not buying and keeping more Heathkit.

This timer works great, very accurate. As soon as I got it, I opened it up for a safety inspection.

Really skilled assembly, with great solder joints, very trim wiring and all components look like new.

It even has one Electron tube!

Draws only 5 watts and is as accurate as I can test with an electronic modern stop watch. I figure +/- 0.1 seconds.

Not all people assembled these kits as nicely as this, so do not trust just any Heathkit device to be the same quality once assembled. Old tube equipment can be dangerous. I put my tube radio collection on a high shelf so I can admire them, but no longer use them.

This timer will be used safely. ymmv

129054129055

[Taija71A]

___

I was wondering where that one went to! :D

Yes... That is most certainly a very beautifully constructed Timer.
(*I like how the Wiring is all 'routed' at nice 90° Angles).



... It even has one Electron tube!

I would guess... That that Raytheon Tube, is perhaps being employed as a simple Shunt Regulated VR (Voltage Regulator) Tube -- In order to keep the 120V 'Line Voltage' constant?

Thanks for posting the pic. Enjoy!
--
Best regards,

-Tim.
_________

[HMG]

Do you remember Lafayette Electronics? From (in my memory) mid 60s.

[Tin Can]

Do you remember Lafayette Electronics? From (in my memory) mid 60s.

Yup, and Allied catalogs. Now I shop Jameco, Pololu and some QST advertisers. I am KD0IJD, but only DX receive AM & SW, as I always have. Not as fun as it used to be.

I made a pirate radio AM station in '65 which I shut down before getting caught. I was wreaking havoc with the local phone system, aka, my inductive antenna...seems phones were ringing off the hook...

[Michael Clark]

Built a Heathkit radio receiver in H.S. in the early 60's in the electronics class, its a shame they don,t offer classes like that any more in the high schools around here. Nothing like a 60cly hum to wake a student up.

[Tin Can]

I learned the hard way not to solder live 120 volt circuits with a wire in my mouth instead of...

[Michael Clark]

It is surprising how fast us young know it all students learn the real facts on the job!! Ha,Ha

[Harold_4074]

Ah, yes---the days of kit-form electronics.

I still have and regularly use an Eico Cortina stereo amplifier from 1968; the chassis is the size of a cigar box, and has about two cubic inches of unoccupied space. A friend who worked in in a high-end hi-fi store in Houston, Texas took it in and reported that according to their distortion analyzer, it was a good as anything in the shop. Sometime in the late 80s, the power supply filter capacitors started to go, so I replaced them with computer-grade electrolytics. I should dig out the manual and see if the power transistors are germanium or silicon...

[Tin Can]

It is surprising how fast us young know it all students learn the real facts on the job!! Ha,Ha

I'm real good with hammers now. My 2 oz is my favorite...

[Michael Cienfuegos]

I'm real good with hammers now. My 2 oz is my favorite...

I have a really nice 32 oz "persuader" for use with stuff which needs to be sacrificed to the gods.

I have a Heathkit PT-1500 Darkroom Timer. I can't remember when I bought and assembled it, but it is still a great timer. I keep it in the kitchen, use it for everything from cooking to developing film.

m

[Tin Can]

I have a really nice 32 oz "persuader" for use with stuff which needs to be sacrificed to the gods.

I have a Heathkit PT-1500 Darkroom Timer. I can't remember when I bought and assembled it, but it is still a great timer. I keep it in the kitchen, use it for everything from cooking to developing film.

m

This is PT-15, perhaps same but different age, maybe older as PT-1500 sounds so much better than PT-109, oh wait, wrong war.

[Corran]

I was tempted by that timer. I don't really like the one I have. But I was worried being home-built it might not be a good build. Guess I was wrong!!

When I was fairly young my grandfather, an air force electrical engineer, gave me a kit made for teens/young adults to build a few different projects - such as an alarm clock and such IIRC. My parents were mad at him because they didn't want me using a soldering iron but I was fascinated with electronics and his workshop so I actually built some of those things and learned a lot. Sadly I lost him soon after to a tragic car accident, otherwise I very likely would've gone down that route or similar rather than music.

Anyway...really cool that there's a tube in there! I didn't think it would need something like that but most of my experience with tubes is audio gear.

[Tin Can]

I was tempted by that timer. I don't really like the one I have. But I was worried being home-built it might not be a good build. Guess I was wrong!!

When I was fairly young my grandfather, an air force electrical engineer, gave me a kit made for teens/young adults to build a few different projects - such as an alarm clock and such IIRC. My parents were mad at him because they didn't want me using a soldering iron but I was fascinated with electronics and his workshop so I actually built some of those things and learned a lot. Sadly I lost him soon after to a tragic car accident, otherwise I very likely would've gone down that route or similar rather than music.

Anyway...really cool that there's a tube in there! I didn't think it would need something like that but most of my experience with tubes is audio gear.

I don't understand the circuit yet...The tube has only 2 pins in use. I guess it's purpose is diode for AC current rectification. So the heating element is not used, no wonder it only draws 5 watts. It has a thermistor for overheat condition, which would only occur if something burned. The case is very tight and fire would have a tough time finding much air or route outside the case. Seems safe enough to me. Controls 350 watts per markings.

[Jim Jones]

Tim apparently is right -- the VT appears to be a voltage regulator, not rectifier. There's at least one diode along the left edge of the interior in photo one. I built and used a Heathkit timer, perhaps this model, until it was destroyed in a darkroom fire. The bar knobs let one set the time in the dark without ever looking at the timer. The analog timer I designed and built lacked that convenience, but could be switched between Focus, Time, and Cancel with a single pole single throw floor switch. Two dual 741 timer ICs controlled everything. It and its schematics were also lost in the fire.

Electronic technology of the 1970s and earlier is still useful. I suppose the performance of solid state multi-band radio receivers far surpasses Hammarlund's magnificent SP-600, but that was obviously designed by men who made engineering an art. The three-tube radio I built in the 40s could pull in stations from around the globe, although it wasn't wired as neatly as the timer pictured earlier. In the 1920s, when radios were still luxury items, some were elegantly constructed and expensive. Soon the superhetrodyne design and pentode amplifiers of the '30s made high performance radios affordable to almost anyone. They lacked the character of the older radios.

[Ray Van Nes]

I have the PT-1500 which I assembled way back in the 80"s. Of course it did not work and had to have the Heathkit dealer fix it. It has worked faithfully ever since. It is programmable so I can have both the enlarger and processing all set up. I recently purchased a second one for my new darkroom for just on the wet side when I am doing film, so I do not have do the exorcist for the one on the dry side.

[Andy Eads]

The photos triggered many dusty memories for me. Kit electronics were my passion as a teen in the 60's. You scored a beauty.

[IanG]

I have a Heathkit Strobe a friend made in the early 70's. Note in the English language usage a Strobe is a stroboscope, this one can give variable rate pulses from a few per second to an interval of about 5-10 seconds, it can also be triggered with a hand switch (push button), I guess it would work off a camera flash socket as well.

Ian

[Ray Drueke]

Ah yes, electronic kits. I put together a Dynaco preamp and a power amp from kit form in the 60s while I was in the Navy. I wish I still had it - they're going for upwards of $300 on the 'Bay these days.

[Chauncey Walden]

I have two of those timers and unfortunately neither is accurate. I seem to recall something like 10-15% off.

[jon.oman]

In my youth, I built many tube based electronic kits. Sadly, although they all worked, I never kept any of them.

[ic-racer]

Randy, you always have cool stuff to post. This is the schematic. The tube (0A2 (http://frank.pocnet.net/sheets/035/0/0A2.pdf)) is a voltage regulator to ensure consistent times. There is a single silicone component (SCR, the black device that looks like a transistor). I repaired an OMEGA timer that was all analog, like this unit, and the only bad component was the SCR.
http://img.photobucket.com/albums/v670/ic-racer/2015/TimerSchematic.jpg

[ic-racer]

When I was younger, I could not afford the fancy Heathkit timer, so I made mine from RadioShack parts using an article in Popular Electronics. Mine used the digital 555 timer chip that had just come out and a 'modern' TO-220 type voltage regulator.
http://img.photobucket.com/albums/v670/ic-racer/timer.jpg

[Tin Can]

Randy, you always have cool stuff to post. This is the schematic. The tube (0A2 (http://frank.pocnet.net/sheets/035/0/0A2.pdf)) is a voltage regulator to ensure consistent times. There is a single silicone component (SCR, the black device that looks like a transistor). I repaired an OMEGA timer that was all analog, like this unit, and the only bad component was the SCR.
http://img.photobucket.com/albums/v670/ic-racer/2015/TimerSchematic.jpg

Thanks!

And double thanks for the schematic!

[BarryS]

That Heathkit is a really clean build--beautiful work. You lucked out with the quality. I recently built a headphone amplifier kit and really enjoyed the process. I'll be starting a second "kit" soon--more like a bag o' parts, so I'll have to do some homework to test the circuit voltages.

http://i.imgur.com/BXUQfQj.jpg

http://i.imgur.com/hzpcHHL.jpg

[Tin Can]

Yes the audio guys still want TUBES!

Great project Barry.

[BarryS]

Thanks Randy. Yes, tubes are very big in the enthusiast audio world. You wouldn't believe the prices of some of the NOS tubes--they're insane.


Yes the audio guys still want TUBES!

Great project Barry.

[Taija71A]

... I recently built a headphone amplifier kit and really enjoyed the process...
___

Barry... You did a very nice job with your Bottlehead Crack OTL Headhone Amplifier Kit.
Congratulations!

Are you perhaps thinking... Of doing the 'Speedball' Upgrade? (*You really should)... :)
--
Best regards,

Tim.
_________

[Corran]

so I made mine from RadioShack parts

Nice. Too bad RS is mostly cell phones and cheap junk these days. And in bankruptcy too. No surprise.

[Jmarmck]

Thanks Randy. Yes, tubes are very big in the enthusiast audio world. You wouldn't believe the prices of some of the NOS tubes--they're insane.
You should see the prices for tube type guitar amps.

[Tin Can]

I have a high end audio store near me. I checked out their low end $2000 tube system, all hooked up and playing my type of music, not rock and roll. Very nice, but I won't spend that much on audio.

My hearing is not that good, sure I can discern differences, but I am more visually aligned than auditory. Tinnitus requires masking sounds.

My 20 year old Aiwa system is good enough for my space, it never is off.

[BarryS]

___

Barry... You did a very nice job with your Bottlehead Crack OTL Headhone Amplifier Kit.
Congratulations!

Are you perhaps thinking... Of doing the 'Speedball' Upgrade? (*You really should)... :)
--
Best regards,

Tim.
_________


Tim--Thanks! I have the Speedball upgrade built and ready to install, but have been holding off because the amp sounds so good as is. Probably install it by the end of the month.

[Taija71A]

Tim--Thanks! I have the Speedball upgrade built and ready to install, but have been holding off because the amp sounds so good as is. Probably install it by the end of the month.
___

I should of known... 'Good Stuff' Barry!
(*Be prepared for a general increase in Dynamics and P.R.A.T.).

Next, you are going to tell me... That you are already 'Tube Rolling' those 12AU7's. :D
________

[Chauncey Walden]

I just discovered something interesting about one of my Heathkit timers which I use as a general light over the sink and as a timed light for contact prints (where the fact that the times are circa 30% off doesn't matter. Anyway I put a little red LED safelight into the fixture that is plugged into the timer as I was going to develop some ortho film and wanted to check on the progression of the development. When I turned the darkroom lights off here is a little red glow coming from the LED. I thought I must have left it on (Focus) instead of (Time) and flicked the timer switch that gave me the bright red LED. Switching back to a definite (Time) gave me the glow again. I used the switch on the fixture and the glow stopped. I switched the fixture back on and placed the plug from it into the Safelight receptacle where it did the same - timer on glow, timer off full red. So there is a continuous bleed of a little juice in the circuitry of the timer into both receptacles. Would not have known without using the LED.

[Tin Can]

I just discovered something interesting about one of my Heathkit timers which I use as a general light over the sink and as a timed light for contact prints (where the fact that the times are circa 30% off doesn't matter. Anyway I put a little red LED safelight into the fixture that is plugged into the timer as I was going to develop some ortho film and wanted to check on the progression of the development. When I turned the darkroom lights off here is a little red glow coming from the LED. I thought I must have left it on (Focus) instead of (Time) and flicked the timer switch that gave me the bright red LED. Switching back to a definite (Time) gave me the glow again. I used the switch on the fixture and the glow stopped. I switched the fixture back on and placed the plug from it into the Safelight receptacle where it did the same - timer on glow, timer off full red. So there is a continuous bleed of a little juice in the circuitry of the timer into both receptacles. Would not have known without using the LED.

I haven't used the Heathkit timer yet, but I have noticed the same thing with a LED safe light with a Beseler Digi-Timer. I haven't noticed this with Time-O-Lites or Gralab 625. I have a few more timers to check and another Gralab 505 on the way.

[Jim Jones]

The schematic in post 21 shows capacitors across the relay contacts, probably to reduce arcing. They could leak enough current to energize low current devices like LEDs.

[Robert Langham]

Anyone got a quick description of how to calibrate these guys? There are three access holes that take a small screwdriver blade. Seems like they advise putting a tape flag on the screwdriver to see how far you turn it. I have two of them that are working but are off on calibration. Seems like I remember that one hole is for the tens, another for the ones and maybe the middle for sensitivity....but I could just be guessing.

Thanks!

[Tin Can]

I sure don't, maybe somebody has a manual.

[Jim Jones]

From looking at the schematic in post #21 and the internal picture in post #1, the calibration adjustments are the two variable resistors on the right of the photo and the sensitivity is on the left. I can't trace out the wiring from just the photo, but trial and error should let you easily determine which calibration adjustment is for which range, and then correctly calibrate the unit.

[Taija71A]

I sure don't, maybe somebody has a manual.
__

The 'posted' Schematic Diagram... Already tells you everything -- That you need to know.
(First)... Grab your LCR Meter... And 'thoroughly' check the Unit.

Then, if everything is still in 'spec' (*But I seriously doubt it)...
You can adjust the appropriate Variable Resistors (R4, R5, R7).
_______

[Robert Langham]

Thanks Jim and all. I have two of the things, one of which I built....uh......35 years ago. I've got the manual.....but not where the timers are! I'm going to flag a little screwdriver and......adjust!

[Duolab123]

Love it! I'm into fixing the old Beseler 45 Dichro S heads . There is a little old Vactrol optical isolator (iso 2 on the board ) that goes on these and when it does the lamp comes on after a random pause or not at all. I have fixed 3 so far. Bought the obsolete parts from some fellow nut on Long Island 13 years ago.
My Brother-in-law's dad built Heath Kit TVs Stereos . I remember building a tachometer for my 65 Chevy Biscayne 230 six 3 on the tree.;)

[Robert Langham]

Breaking my own rule of never posting without including an image....there aren't any Heathkits in this shot, but there will be some in the image's future! Thanks to everyone for input.

130996

[Lee Rust]

Compare Heathkits to this:

http://www.radioshack.com/littlebits

We live in a plug & play world now.

[Robert Langham]

Got them whipped into shape. Can't seem to do better than a two-second overage at 60 seconds, but as long as it is consistent, that should be close enough.

131021

Might have found someone who will install LEDs in my Zone VI head....now THAT would be a nice thing.

[Tin Can]

Got them whipped into shape. Can't seem to do better than a two-second overage at 60 seconds, but as long as it is consistent, that should be close enough.

131021

Might have found someone who will install LEDs in my Zone VI head....now THAT would be a nice thing.

Would you confirm which holes are which adjustment?

Just for the 'permanent record'.

Thanks

[Snoopy-16]

I have just bought the PT1500 Heathkit darkroom timer. It was previously used in the USA. As I’m in Australia, I need to convert it to run on 240V. I have found a manual on EBay UK & the seller has just posted it, but has just told me it’s going to take 12 weeks to be delivered!
Does anyone have the build manual & could post / email the relevant section on setting the transformer to switch from 120V to 240V that you would not mind sharing, so that I can get this timer working now?
Thanks in advance 😊

[Tin Can]

Sorry no manual

Good luck, in the end I gave up on my HeathKit, it was a romantic notion


I have just bought the PT1500 Heathkit darkroom timer. It was previously used in the USA. As I’m in Australia, I need to convert it to run on 240V. I have found a manual on EBay UK & the seller has just posted it, but has just told me it’s going to take 12 weeks to be delivered!
Does anyone have the build manual & could post / email the relevant section on setting the transformer to switch from 120V to 240V that you would not mind sharing, so that I can get this timer working now?
Thanks in advance 😊

[Bob Salomon]

I have just bought the PT1500 Heathkit darkroom timer. It was previously used in the USA. As I’m in Australia, I need to convert it to run on 240V. I have found a manual on EBay UK & the seller has just posted it, but has just told me it’s going to take 12 weeks to be delivered!
Does anyone have the build manual & could post / email the relevant section on setting the transformer to switch from 120V to 240V that you would not mind sharing, so that I can get this timer working now?
Thanks in advance 😊

It also needs to run on 50hz down there or times will be 20% off.

[John Layton]

...could work to compensate for dry down! :rolleyes:

[Paul Ron]

the error in the time is probably bad capacitors in the timer section.

i recently took out my old heath kit tube osciliscope i built as a kid in the 60s. its working just fine but its just not as sexy as my old duel trace techtronics that weighs in at 60lbs all tube.

you can check the caps esr n circuit.

see if your timer manual is here...

https://www.vintage-radio.info/heathkit/


edit... its there as photo timer if you scroll past the ocsiliscopes

[MrFujicaman]

Randy, I don't know who built that timer, but I'd guess he's OCD! I've seen factory made stuff that wasn't that neatly made!

[Snoopy-16]

It also needs to run on 50hz down there or times will be 20% off.

Yep Bob, you are right. I eventually received the manual, & it didn't take long to convert the transformer to run on 240V, but the 50hz / 60hz issue is real. Like you said, it is running about 20% slow.

Is there any known work a rounds for this?

[Duolab123]

Yep Bob, you are right. I eventually received the manual, & it didn't take long to convert the transformer to run on 240V, but the 50hz / 60hz issue is real. Like you said, it is running about 20% slow.

Is there any known work a rounds for this?

Money :o

[revdoc]

I think the only easy way to get a 60Hz AC supply is with an inverter. I don't know how well that would work; your timer probably expects a clean 60Hz input, and an inverter might generate some noise.

[Peter Lewin]

I’m sure I am stating the obvious, but why don’t you re-mark the dials with times adjusted for the 20% difference, so 1 minute would be 1:12 etc. what you need for printing is consistency, not timing in one-second or one-minute intervals.

[Chauncey Walden]

Would you confirm which holes are which adjustment?

Just for the 'permanent record'.

Thanks

Could someone answer this question, please?

[LeonardDowd]

a device that has proven itself from the best side not a few times, proven by time and experience. At the present time, in fact, everything has to be rebuilt by yourself, adding your own components.

[Paul Ron]

Would you confirm which holes are which adjustment?

Just for the 'permanent record'.

Thanks


its in the manual.....

https://www.vintage-radio.info/heathkit/

its a pdf as PT-15

scroll down past the oscilloscopes.

[Chauncey Walden]

Thank you.

[Bernard_L]

Quote Originally Posted by Snoopy-16 View Post
I have just bought the PT1500 Heathkit darkroom timer. It was previously used in the USA. As I’m in Australia, I need to convert it to run on 240V. I have found a manual on EBay UK & the seller has just posted it, but has just told me it’s going to take 12 weeks to be delivered!
Does anyone have the build manual & could post / email the relevant section on setting the transformer to switch from 120V to 240V that you would not mind sharing, so that I can get this timer working now?
Thanks in advance 😊

It also needs to run on 50hz down there or times will be 20% off.
Looked at schematic posted by Paul Ron (for the PT-15) and there is nothing there that depends on the mains frequency. Indeed, the specs section explicitly states 50/60cps.
210756
But in case your PT-1500 is significantly different from the PT-15 and does depend on mains frequency, what is the real drawback of running 20% slow, if used as an enlarger timer? You do test strips, anyway, right? So why not time all your exposures in pseudo-seconds? As long as the times are consistent between test strip and actual exposure, you should be doing fine. A 60Hz inverter would be overkill.

[Paul Ron]

that timer depends on capacitors... R/C circuit. more than likely, caps c3 c4 and c5 should be changed and that may solve the inaccuracy problem.

otherwise as long as its consistantly wrong, leave it.

[Bernard_L]

Adjustment. Read The Fine Manual
https://www.vintage-radio.info/download.php?id=641
Page 15-16 the adjustment procedure is described (R4 and R5). I would bet that the range of adjustment is enough to cover 10-20% and get it down to 1% or better. Achieving this with capacitor substitutions would be a lot more difficult (there are no continuously variable capacitors in the µF range); the schematic seems to be designed thoughtfully.

Even if absolute accuracy is almost irrelevant, the adjustment is necessary to ensure at least the consistency of the x1 and x10 switches.

[Paul Ron]

Ya dont need variable caps or make substitutions... replace them with the same values as in the diagram. Simple unsolder job. As caps get old they dry out n qct more like resistors n that causes them to be unstable, discharging too slow or too fast n not hold their charge properly as designed. Those caps are easy parts to find, standard value electrolytic. Heathkits are designed for easy access to the parts so not much experience in electronics is needed to build them.

[Bernard_L]

Those caps are easy parts to find, standard value electrolytic.
I looked up in the Mouser catalog for the value 2µF (that is C3). In 2020, the vast majority of caps available for that value are film capacitors. Tolerances listed are 10% or 5%. That is not good enough (without trimming adjustment) because 10% of a step on the x10 switch is... 100% of a step on the x1 switch.

Look at electrolytics as Paul Ron proposes. The typical tolerance for 2µF aluminium electrolytics is -10%+75%(!!). For Tantalum electrolytics, the tolerances are better, typically 10%...20%; except 2µF is not available, only 2.2µF (a truly standard value from the E5 series).

My recommendation: follow indeed the advice of Paul Ron to replace the capacitors, as the original ones are old aluminium electrolytics. Replace them with film capacitors of proper rating (at least 200VDC). Use the available adjustment resistors to bring the timings closest to nominal.

[Paul Ron]

no need to get crazy with "better.".... all you need are the same or similar parts to replace them with to be as accurate as heathkit states in its specs for the unit... you arent building to mil spec. its a consumer unit and does have an adjustment resistor for each range. new caps will preform more consistantly than the old parts. the timing depends on how reliably the caps charge n discharge.

also clean the trimmers (adjustment pots) with some contact cleaner n excersize them a bit.

[Snoopy-16]

Looked at schematic posted by Paul Ron (for the PT-15) and there is nothing there that depends on the mains frequency. Indeed, the specs section explicitly states 50/60cps.
210756
But in case your PT-1500 is significantly different from the PT-15 and does depend on mains frequency, what is the real drawback of running 20% slow, if used as an enlarger timer? You do test strips, anyway, right? So why not time all your exposures in pseudo-seconds? As long as the times are consistent between test strip and actual exposure, you should be doing fine. A 60Hz inverter would be overkill.

I think you are right. I think I am just trying to get perfection when it's not necessary. What you suggest (in using 'pseudo-seconds') works fine. I do have an old exposure computer, which gives a close estimate of the exposure time, which I can still use if I calculate the error into the mix, but other wise, the timer works fine by giving constant exposures, even if it's not using a standard constant.

[Bernard_L]

Update. I looked for a manual for your PT-1500, as distinct from the PT-15 around which much of the recent discussion revolved. Only found a picture.
210849
which tells me it is a completely different animal. (1) All the discussion about RC time constants and aging capacitors is most probably void, and the available manual for the PT-15 is not relevant. (2) Contrary to what I stated (based on the PT-15 schematic) it is likely that the mains frequency is the basis for the timing, as you had stated; so the +20% is not a coincidence. The good news is that the consistency between the x1, x10, etc scales is a non-issue. Also the exposure computer: it must be calibrated before being used, so why not in pseudo-seconds.
If I were in your shoes, I would peek under and inside the box for a switch or jumper for a 60/50Hz change. Heath sold worldwide, and it would not be economic to make two versions of the circuit; the transformer being a different story, with significant economic saving in having a single-voltage component, either 110 or 220V.
As an aside, I have embarked into the construction of an Arduino based timer following the description given there: https://eliadarkroom.wordpress.com/

[Paul Ron]

and there ya have it! its a newer model.

there must be a switch or jumpers inside for 120/220 operation.

but almost all electronis timers use either RC or crystal or some sort of frequency generated reference signal n not depend on mains frequency since a power supply is regulating circuit voltage, converted to dc for the descrete components filtered through a rectifier n diodes.. old mechanical clock motors depended on mains since they operated directly off mains ac voltage. your pt-1500 has an lcd.. and more than likely chip controled and that is not mains dependant.

still... old caps are the general cause of most irregularities in RC biasing regardless of what type of chip or crystal. but because it has calibration pots to take up the slack, it may still be within calibrating tolerances plus being newer, the caps may still be up to snuf.... consistancy is your clue.

the search for the manual continues... there has to be one floating around the net.

. can you get a picture of the circuit board?

edit...
microprocessor controled self test....

found this...
http://nostalgickitscentral.com/heath/products/misc/pt1500_cal.html

[Snoopy-16]

210895
and there ya have it! its a newer model.

there must be a switch or jumpers inside for 120/220 operation.

but almost all electronis timers use either RC or crystal or some sort of frequency generated reference signal n not depend on mains frequency since a power supply is regulating circuit voltage, converted to dc for the descrete components filtered through a rectifier n diodes.. old mechanical clock motors depended on mains since they operated directly off mains ac voltage. your pt-1500 has an lcd.. and more than likely chip controled and that is not mains dependant.

still... old caps are the general cause of most irregularities in RC biasing regardless of what type of chip or crystal. but because it has calibration pots to take up the slack, it may still be within calibrating tolerances plus being newer, the caps may still be up to snuf.... consistancy is your clue.

the search for the manual continues... there has to be one floating around the net.

. can you get a picture of the circuit board?

edit...
microprocessor controled self test....

found this...
http://nostalgickitscentral.com/heath/products/misc/pt1500_cal.html


Hi Paul Ron,
I now have the complete manual for the PT-1500. I purchased one from England & it showed how to convert from 120v to 240v by switching some jumpers, but I couldn’t see anything about setting the Hz value. I am away from home for the next week, but I can scan the manual & post it here when I get home. I don’t know much about electronics. The voltage switch was obvious & easy
to see, but not so for the Hz issue. Perhaps someone who knows what they are looking at would know more.

I do have these photos on my phone of selected manual pages, but I’m not sure the quality will be good enough. I’ll post them anyway...