can I use this OT?

[dmartn149]

I've got this old radio. I was thinking I would use the transformers in a guitar amp build. I've built a couple of small amps, but I didn't really design them, and there is so much that I don't know. So the PT looks like it will work, but I don't know about the OT. 625 ohms
rca.pdf

[The Dude]

Sure. Why not? The transformers worked in the radio.

[dmartn149]

Sure. Why not? The transformers worked in the radio.

well sure, but I'm not just plugging a guitar signal into the radio. About all that would be the same is 2 6v6's and cathode bias.

[The Dude]

Understood, and not trying to be a smart a$$, but the OT doesn't care much about the preamp. If you're building the same output section, then the transformer will work just fine.

[dmartn149]

Ok, and the speaker should be not too far off, impedance wise, right?

[dmartn149]

Thanks, Dude.

[Justin Thomas]

As long as you just leave the output section pretty much the sane & use the same impedance speaker (cuz I don't know that a radio speaker would work all that great for guitar) the transformer won't care. It's not the resistance on either winding that really matters; just the ratio between the two. So, the tranny isn't changing, the output tubes aren't changing, & the speaker load isn't changing, so you should be just fine.

There are odd speakers out there that are something nuts like 32Ω or other weird stuff. But I doubt you've got that. Just stick a meter on the speker & measure the resistance. 3-5 =4, 6-9 =8, 12-16 =16. Close enough. As Enzo would say, "it's just a guitar amp, not a NASA moon rocket." Precision isn't that important. Heck, it's possible that since it IS from a radio, thst it IS more precise than any guitar amp!

Good luck, rawk out, & most importantly, have fun!

Justin

[dmartn149]

The plan is to use just the transformers, not the speaker, chassis or any of the old circuit. I thought I'd start with a 5E3 deluxe-ish circuit, then tweak if needed. I guess now I need to figure out what the impedance of the radio speaker is.

Thanks.

[Chuck H]

I might suggest using a diode rectifier (315V approx). Or at least a gz34/5ar4 (305V approx). The original 6x5 won't handle the current of the hotter bias of a 5e3 type design very well. Using a 5y3 rectifier as per the 5e3 design would have your HV sagging down to something like 260V. The high-ish resistance of the PT secondary should give you plenty of "sag" without a rectifier tube. The diode rectifier would also allow you to use a larger input filter. This might help tighten up the LF wich might suffer a little with the lower plate voltage.

Knowing the speaker impedance will be important, as already noted.

[dmartn149]

Thanks Chuck. Yes, I was planing on building a SS rectifier.

[nosaj]

I might suggest using a diode rectifier (315V approx). Or at least a gz34/5ar4 (305V approx). The original 6x5 won't handle the current of the hotter bias of a 5e3 type design very well. Using a 5y3 rectifier as per the 5e3 design would have your HV sagging down to something like 260V. The high-ish resistance of the PT secondary should give you plenty of "sag" without a rectifier tube. The diode rectifier would also allow you to use a larger input filter. This might help tighten up the LF wich might suffer a little with the lower plate voltage.

Knowing the speaker impedance will be important, as already noted.

Also I'd hope the transformers are good.. I think 6x5's were possibly known for taking out transformers when they shorted and shorted they did.https://canadianvintageradio.com/cvr...blematic-tube/https://canadianvintageradio.com/cvrs-forums/topic/the-6x5-a-problematic-tube/

nosaj

[dmartn149]

Thanks Nosaj. I had heard of that, so I was going to change the rectifier from the start. Then I noticed the relatively low voltage from the PT and decided on SS recto. I'll make sure the transformers are good before I get into it. Just thinking and planning now.

[nosaj]

Thanks Nosaj. I had heard of that, so I was going to change the rectifier from the start. Then I noticed the relatively low voltage from the PT and decided on SS recto. I'll make sure the transformers are good before I get into it. Just thinking and planning now.

Might I suggest going with the tube rectifier, then taking a octal socket wired with diodes. You just might like the low voltage sag sound. I know I did on the junk box one I built.
nosaj

[Chuck H]

I built a little 2x6v6 amp with 300Vp from parts of an old phonograph. I really liked the overdrive. The original amp used a 5y3 and had something like 275Vp so I switched it for a 5V4 and got my 300V. If I'd had a 5ar4 on hand I'd have used it instead.

But as far as I know that PT doesn't have a 5V winding. So about the only rectifier option would be a 6ca4. Which won't drop any voltage to speak of.

Probably another good reason to use a tube rectifier (6ca4) is that the filament winding is designed for a butt load of tubes. If you only load it with a couple of tubes your filament voltage may be grossly higher than spec.

It should be easy enough to check the transformers since the DC resistances are indicated on the schematic If the windings ohm out and there are no shorts between windings I'd say you're good to go.

[dmartn149]

But as far as I know that PT doesn't have a 5V winding. So about the only rectifier option would be a 6ca4. Which won't drop any voltage to speak of.

What about a 6x4 My Champ-ish home made amp uses a 6x4 rectifier, and I have spares. How difficult is it to implement dual rectifiers, switchable?