trinityamps.com

I haven't been on the forums here for years now but I know there are very helpful people on here so thought I'd ask for advice here.

So the other day I had the unthinkable happen. While jamming through my mostly original 1950's Fender Champ, it shut off. To make a long story short, with some help from my dad we've figured out its a shorted power transformer. I have to say its very disheartening because I like the amp, not to mention its a little valuable piece of amplifier history.

So here's my question: What brand of replacement transformer would you recommend? The 2 major ones that come to my mind would be Heybour or Mercury Magnetics. Any other suggestions?

Thanks for your help.

Trinity Tramp transformer maybe but without knowing more about your amp to compare specs I can't say for sure.

Other options for transformers that I have used are:

ClassicTone http:\\classictone.net (I've used a couple in projects for other people and they seemed happy with results).

BBQ

There are others but I can only comment on what I have tried. Google it.

Personally I'd research the amp a bit to learn exactly what it is (there were circuit variations) and that may help narrow down what you need but that's just me. If you find a shop or music store around that has or knows somebody who is a 'real' tube amp guy you may be able to get some help.

If Stephen doesn't have one that works for you, I strongly suggest Hammond. The others listed are good too, but for power transformers that will be made "to spec" of the original, Hammond is the best bang-for-the-buck and their reputation is top-notch.

https://www.hammfg.com/electronics/transformers/classic/290.pdf

What makes you think it's a shorted power transformer? And if it is for sure, make sure you know why it shorted before you just drop a replacement in there because it may just happen to your new $$$ transformer too.

My dad helped me troubleshoot it, taking measurements with a multimeter at different spots in the circuit. My dad has about 40 years experience with electronics, I know little so I can't recall all the things we tested but that is the result he came up with. The only thing I can recall for sure is the amp will blow fuses even with no tubes in it so we were able to isolate problems to the main power section. What we measured from there I can't remember. As far as it being something else that caused it to short, I don't know. I mean, it IS a 60 year old transformer so it very well may have just died from old age I guess.

I'll have to look into the Hammond transformers too, I know they are good as well.

Check out this resource...
http://www.geofex.com/ampdbug/ampdebug.htm

Specifically this section if the problem is fuses blowing...
http://www.geofex.com/ampdbug/fuseblow.htm

Don't get me wrong, you may indeed have a bad transformer but have the power supply filter capacitors ever been replaced? That would be my #1 suspect for an amp that old. In fact, if they have never been replaced, or even if they haven't been in the last 20 years or so, I would start with that because they need to be replaced anyways. And it might just solve your issues and save you from an expensive transformer purchase.

60 year old transformers are nuthin... people gut vintage radios and organs just for their transformers all the time. They are a great source of cheap iron.

I'll take a look at those links you gave me.

The filter caps were replaced with new ones about 8 years ago.

Heyboer make them for a lot of people (Mojo for example) . The tramp PT wont work because it has no rectifier heater tap. Problem is you wont know what your real voltage was since its gone south. Unless you documented it previously.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Any suggestions for figuring out what the voltage should be? I never documented the voltages when I replaced the original caps. Mojo has 2 different power transformers listed for Champs, one with 290 volts and one with 330 volts.

Can you find a Fender partnumber on the shell. I would remove th epower transformer and measure the mounting holes and make sure whatevr you buy will fit. For my money, I'd go with Mojo's Heyboer model.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The interesting thing about this amp is that when I got it, it was 100% original and untouched. From the date stamp on the chassis I determined it was made November 1954. This means that it should be a wide panel model, but its a narrow panel model which came out in 1955. So I assume it was early production for the new 1955 year.

No part #'s on the transformer. The only markings on the original transformer are "OP-250B" and "606036". From some of the research I did this suggests that the manufacturer was Woodward-Schumacher and date code of 36th week of 1950. Interestingly both transformers as well as the original speaker all date from 1950.

None of this help me figure out voltage though, unfortunately.

Narrow panel, so it's a 12AX7 preamp tube, right? And no tone knob - just volume?

If it's a 12AX7 and no tone knob, then the next question is does it have a filter choke or not?

Filter choke means it's a 5E1, no choke means it's a 5F1.

5E1 used a 250-0-250 power transformer. Here is a good wrietup on the 5E1 power supply... https://www.ampbooks.com/mobile/classic-circuits/fender-champ-5e1-power-supply/
A Hammond 270CAX or equivalent would fit the bill.

5F1 used a 275-0-275 I think. Here's how I came up with that...
According to the 5F1 layout Fender shows 340V at the first filter cap. Add 50V to that (the typical voltage drop from a 5Y3 rectifier at those low voltages and current draws)... 340V + 50V = 390V

With a full-wave rectifier on a center-tapped transformer, divide that by 0.71 to get the un-rectified AC input voltage... 390V / 0.71 = 549.3V

Since it's a center-tapped transformer, divide that by 2: 549V / 2 = 274.5V

So, a 275-0-275 transformer for a 5F1 is what you are after to stay true to the original. Try a Hammond 270BX or equivalent.

Heyboer probably has equivalents I would think.

One really cool thing about the Hammond power transformers is that they come with both a 115V and a 125V primary hookup. That gives you a better chance at getting the secondary voltages historically correct since wall-voltage is higher now than it was in the 1950's.

You are lucky. I am trying to retype my machine by myself and I must say that it is not easy. In any case, friends will come to help me next week.

While Heyboer and Mercury Magnetics are both reputable brands for replacement transformers, there are a few other options you might consider as well. Here are a few suggestions:
ClassicTone: ClassicTone transformers are known for their quality and are often used as replacements in vintage amplifier restorations.
Hammond: Hammond Manufacturing produces a wide range of transformers, including those suitable for guitar amplifiers. They have a good reputation for their products.
Triode Electronics: Triode Electronics offers replacement transformers for vintage amps and is known for their attention to detail and quality construction.
tunnel rush

When it comes to replacing a power transformer, you want to ensure that you get a high-quality replacement to maintain the amp's performance and value. Heyboer retro bowl college and Mercury Magnetics are both reputable manufacturers of replacement transformers, and either one should work well for your Fender Champ.