Find 60s Tempo Tube Amp Schematic (see picture) Tubes are 35w4, 12AU6, and I believe a 50C5.

[Shawn]

Thanks for any help. I scoured the internet and I have yet to locate.
Happy New Year!

[Chuck H]

Well I couldn't find a schematic but the panel is very like the Harmony H400A with three inputs, volume and tone. Same tube line up. Tempo amps were made in Japan and probably copied circuits from other "affordable" brands like Harmony, Unicord/Univox, Valco, etc. The circuit will be very simple and it shouldn't be hard to see if your amp is the same as the Harmony. Or you could just draw up a schematic for yourself by circuit tracing.

That said I didn't post the H400A schematic because there's no certainty it applies here. You can find it on line though. And THAT said, your amp is what's called a "widowmaker" design. There is a risk of shock or electrocution with these designs and you should research adding an isolation transformer and a safety ground to the amp before using it. That information can be found here on the site with a little searching.

[Shawn]

Chuck,
Thank you for the information.

It is interesting you mention the H400A schematic as I looked at that as well. I notice the H400A utilizes a transformer in the heater circuit (T2) which I do not have with the Tempo. I am not beyond tracing the circuit as well. The reason I started down this rabbit hole is I wanted to confirm the power tube is supposed to be a 50C5 and confirm my heater string would consume the ~117v line voltage. Given 35+12+50=97v and 117-97= 20 volts. I should find a dropping resistor of ~133 ohms and about 7 watts capability. I found an odd looking resistor that looks to be labeled (red, black, brown) and measure around 200ohms. 200 ohms appears a bit large given the tubes being used.

I also appreciate you including the safety info.

https://antiqueradio.org/safety.htm

What I typically do is install a polarized plug and ensure the hot is wired directly to the switch. Do you believe this strategy to be viable? I believe this is consistent with the article I attached from antiqueradios.

I was going to upload a picture of the funky resistor but it says I have exceeded my size limit.

[g1]

What I typically do is install a polarized plug and ensure the hot is wired directly to the switch. Do you believe this strategy to be viable? I believe this is consistent with the article I attached from antiqueradios.

In radio, the operator is not holding the ground (guitar strings) in their hands, so it is a different ballgame and you can get away with plastic knobs and polarized plugs for safety.
For guitar amps you need the isolation transformer.

[nosaj]

Just my opinion here but I wouldn't pay 350 for it. it will like be super cheap construction and not sound super great . not even a good platform for experimentation.
nosaj

[Shawn]

Thanks Nosaj. Someone gave it to me and I thought I would get it going for fun. I appreciate all the insight here. I included a picture from Reverb just to share what it looks like. Thanks!

[Chuck H]

Jason's right that you wouldn't want to pay $350 (but free seem just fine ) HOWEVER... Pay no mind to his comment about it not sounding super great I've been blown away occasionally by what would be considered cheap practice amps back in the day. Tone is subjective so it's something you'll decide for yourself of course. And, again...

Isolation transformer and earthed chassis!!! Like g1 said, when playing an electric guitar you are actually connected to ground whenever you're touching the strings. Which you should be most of the time (if you needed playing advice ). If that ground isn't EARTH then it'll never be safe.

[nosaj]

What have you done to it so far? power up, etc?
Recommend building a dimbulb tester https://antiqueradio.org/dimbulb.htm

Here is the isolation transformer https://www.tubesandmore.com/product...00-ma-1-x-115v

Here is an article for you on widowmakers https://robrobinette.com/Widowmakers.htm\
nosaj

I'm finding that its possible that it may be Teisco

[nosaj]

https://lectrolab.wordpress.com/lect...ls/widowmaker/
A visual rep of how you are actually in danger.
nosaj

[x-pro]

AC and DC currents up to 1.5 mA cause slight cramping of the fingers.
This 1.17mA will only tickle your fingers.

[Chuck H]

AC and DC currents up to 1.5 mA cause slight cramping of the fingers.
This 1.17mA will only tickle your fingers.

Being 55 I grew up with two prong AC plugs on old "record players", HO train power supplies, tape decks and such. I know too well the tickle you're talking about. We use to do that on purpose!!! Once discovered and realizing it wasn't fatal my brother and I would take turns holding the tickle points on these devices and trick our friends into doing the same. It's only now, knowing the reality of the matter that I realize how foolish that was. One shorted capacitor and what was a fun game of "Check this out." becomes potentially FATAL!!!