Building 5F1 Champ Style Amp

[DrGonz78]

My question is in regards to finding a power transformer. I already have a Hammond 125DSE that I could use for the OT. I am looking to buy some things from Mojotone to get this amp really going. The Mojo site is on back order of there champ style PT's, mojo759.
Mojo Transformers » Tweed Champ Power Transformer (120V Only)

I was thinking about getting this one since it is readily available...
Fender® replacement power transformer, 325-0-325 V, 70 mA [XFR-FP-22772] - $49.95 : NewOldSounds.com

Right now I know I will have to drill a hole to be able to fit the Hammond OT on the chassis that I am using. I am not sure if that champ replacement PT will fit on my chassis. It is the same chassis that you get from Mojotone. Does anyone know if that Fender part# 125P1B, 022772 from New old sounds will fit? Thanks!

[big_teee]

I like the classic tone transformers.
They are a good value and made near chicago.
Fender Champ, Tweed Princeton, Bronco Amplifier Transformers - 5W Single Ended Style Amplifier Transformers By ClassicTone
There are two distributors for them.
I like the Amps parts direct the best.
Their shipping is usually the cheapest.
Fender Style Champ & Princeton 40-18019 - Amp Parts Direct
That is where I bought the iron for the 50 watt head I built earlier.
Good Luck,
T

[g1]

Both the 022772 and the MOJO759 are listed as mounting on 2"x2.5" centers. So if the mojo759 transformer is supposed to fit that chassis, the other should also fit.

[ron vogel]

I like the classic tone transformers.
They are a good value and made near chicago.
T

I literally work across the street from them...original OEM supplier to valco in the 50's/60's amps...and they still make them the same way they did in the Valco days...on the same equipment. Place is a dump and smells like a dog kennel, but the transformers are nice. I stop in there from time to time to talk with the engineer.

[DrGonz78]

Hey thanks for the replies, this is good info. Basically I have been building this thing a little bit at a time. Could have ordered a kit, but this way it will make me do some thinking as I put it together.

[big_teee]

I like the Classic Tone products, but I also like their Website.
They do a better job of showing what is available, and what fits what, and offer Project transformers.
They do a good job of offering drawings of all their transformers, and cut out drawings.
Here is a XL Doc I keep on my laptop and go over often.
http://www.classictone.net/ClassicTo...e_Database.xls
T

[g1]

The Classic Tone replacement for 022772 would be 40-18019
Fender Power Transformer, Champ, Princeton, Vibro-Champ, Bronco, Harvard, 125P1B & 022772, 120V

[DrGonz78]

Well I already had the Hammond OT, chassis, cabinet and mojo speaker. Now I just ordered all the small parts and tubes. Gonna order the classic tone PT and that should do it! Thanks again guys for the helping support.

[DrGonz78]

So I am in the process of building this amp and I have a quick question. There are two green wires and a third green/yellow wire for the 6.3v heater voltages. So I would assume that I need to ground the green/yellow center tap, but was wondering if there is a grounding rule to follow? Basically, I will ground the red/yellow HT center tap mated with the safety ground from the wall, which is easily mounted to a lug on the PT. I have a star ground lug where all my other grounds will go from the fiber board layout of the circuit. Should I be grounding the green/yellow wire to the circuit star grounding or along with the red/yellow and saftey ground? Is there any cardinal grounding rule to follow here?

[ric]

I have read to grnd chassis as close as possible to where outlet enters, direct to chassis, not on PT mounts. Each "star" of grnds is then grnd'd at PT end of amp, at same place as filter cap supplying that node. Except 1st stage filter cap which is best located and grnd'd at front end of amp. Does this square with what the pros on this site know?

[g1]

As far as the safety ground (3rd prong) goes, it is supposed to be a dedicated ground that serves no other purpose. So it should not be connected to any other ground terminals or other hardware mounting screws. So it should not be going to a PT mounting bolt, rather to a screw that serves no other purpose. Every other ground should connect elsewhere. And the green (or ground) wire of the AC cord should be left longest, so if the cord is ripped out, the ground wire will be the last one to disconnect.

[Bruce / Mission Amps]

Ground your power cord's wire all by itself and make it the longest of the three power cord wires so it is the last to come off the chassis if it gets yanked out.
Your Red/Yellow, high voltage secondary center tap wire needs to be connected to the negative lead of the first main filter cap and then grounded to the chassis.
The green/yellow wire can be connected to the the power tube's cathode biasing resistor to feed a little positive DC voltage from the power tube into the center tap of the filament supply for slightly less noisy amp.

[ric]

Bruce, is the htr grnd to go to the cathode of the output tubes, or to the point that they ground to the chassis? G, thanks for the very important point about ground wire relative length.

[g1]

To the cathodes. This will elevate the heaters a bit from ground and usually results in less noise than grounded heater CT.

[DrGonz78]

Okay I knew I would get some great answers!! So safety ground dedicated to it's own mount and longer than hot/neutral wires as a safe guard. Secondary center tap (red/yellow) wire goes to negative end of first main filter cap, then to ground. This is making more sense and I am glad to have asked this question. I will check back for more info to Ric's question about where the green/yellow CT should connect to the output tubes cathode resistor. Thanks for the help thus far, much appreciated!

Edit: I see G-1 just posted an answer, nice!