Can I use a Champ P-TF22905 Output Transformer as a Reverb driver?

[5thumbs]

Building a scratch build and have a Champ OT sitting around gathering dust and don't have a reverb transformer available. Can I use this transformer as a reverb tank driver instead? The impedance would be off a little bit, but would it really matter when all I need is to shake some springs? I think the Fender Reverb Driver is: P-TF22921 with 25k ohms:8 ohms ratio. The Champ transformer would be 17.5K ohms:8 ohms.

[Enzo]

You have the part, and it has four wires. Tack the four wires into the circuit, then YOU can tell US what happens.

[Leo_Gnardo]

The impedance would be off a little bit, but would it really matter when all I need is to shake some springs?

I have a feeling it will work just fine. I like your "go with what you got" attitude! We have people here who figure out their reverb circuits to the 13th decimal place, not that there's anything wrong with that... Heck yeah, shake those springs and put a little grease on your guitar tone!

Also I've often wondered how a reverb transformer would sound driving a speaker. One of these days I'm gonna give it a try. Can't be any worse than a Champ, right? As in, don't expect much low end.

[Enzo]

SImple enough, pull the drive end cable from the reverb pan, and connect it to a speaker.

[Leo_Gnardo]

SImple enough, pull the drive end cable from the reverb pan, and connect it to a speaker.

I know, simple enough, right? And yet I've never done it. Next time I have a Fender reverb amp of any sort on the workbench, for sure! Gonna give my JBL K120 test speaker a real workout.

[Enzo]

MAybe start with an attenuator, wouldn't want that watt to risk the speaker.

[5thumbs]

I am building a combo chassis that is very tight. Reverb transformer has to be mounted on the back side with access to mounting covered by the tag board. So once I wire it in, it will be difficult to remove. If it had been as simple as "tack four wires" I would have done it and not have troubled anyone. I was just hoping that someone had experience doing this and tips on any mods needed to make it work.

[Leo_Gnardo]

MAybe start with an attenuator, wouldn't want that watt to risk the speaker.

Thanks matey, you are the voice of experience!

I was just hoping that someone had experience doing this and tips on any mods needed to make it work.

It may take a while to get a response from somebody who actually has done what you propose. IF indeed we have someone who has. But I don't see that it would be a problem. Either go with what ya got, or if you're all that worried, order up the reverb drive transformer. I know, you're champing at the bit, gotta build that amp now!

[mozz]

Some champ transformers are 17k, other are lower, like 8k. Just use a 12at7 to drive the reverb. Be sure the tank is a low impedance input too.

[5thumbs]

Hey Mozz,
The champ transformer is 7k into 3.2 ohm, so that’s where I got 17k into 8 ohm

[Chuck H]

Some champ transformers are 17k, other are lower, like 8k. Just use a 12at7 to drive the reverb. Be sure the tank is a low impedance input too.

Pretty sure there were no 17k Champ output transformers. They are all pretty much 8k. But since the Champ OT has a 4 ohm secondary you would double your primary impedance running it into an 8 ohm load.

[Leo_Gnardo]

Pretty sure there were no 17k Champ output transformers. They are all pretty much 8k. But since the Champ OT has a 4 ohm secondary you would double your primary impedance running it into an 8 ohm load.

And if you're worried about overcurrent in the 12AT7, use a 2k2 resistor in the cathode. Your option to bypass with a cap or not. With the bypass cap, likely you'll be slappin' that tank for full surf reverb. Leave it out for a mellower reverb overall. Hey, you could put in a switch and choose one or t'other as it suits your mood.

[Chuck H]

And... Since this is build in progress you could omit the parallel triodes reverb driver and use a single triode instead. That would get you a closer match impedance wise and save you a triode for some other function. I used a 12dw7 for a single triode driver in my last reverb amp. The lower mu triode in that tube can make ample power for driving the tank and the higher mu triode is a good recovery stage. I got really satisfying results using a "standard" reverb transformer. You're Champ OT would be a better fit.

[mozz]

I think the very first ones in the tweeds had 3 different transformers. The 17k is the smallest. I have one here from 1959 with problems(shorted turns). Guy was using a 8ohm speaker, i guess the voltage swings were real high. I think classictone list the 3 replacements.