Baldwin conversion - what to build?

[Pixel]

I have a Baldwin chassis with power and output transformer. It originally had four 12AX7, four 6BQ5 and a 5U4GB. It also had two output channels but I have put the other output transformer somewhere clever and can't find it at the moment. I don't have any of the tubes either.

The power transformer measures 310-0-310 and has both 5V and 6.3V heaters as well as some mystery outputs I haven't measured yet. The output transformer has a 37-1 turns ratio.

I have built lots of SS stuff from scratch, etched my own pcbs, and have recapped SS and tube amps.

I was thinking of trying Sluckey's Vox AC 15. Is that foolish for a first time tube build?

[eschertron]

Based on the Baldwin chassis I got some time ago, I'd wager that one set of 'mystery outputs' from the PT is a 12.6v winding for the 12AX7 heaters.
If the PT in yours was powering a quartet of EL84s, then I'd presume that you could make a pair scream for mercy that's what an AC-15 is for, right?
I will also suggest that you pick a rectifier tube based on your measured/desired B+. Keep us posted!

[vintagekiki]

I was thinking of trying Sluckey's Vox AC 15. Is that foolish for a first time tube build?

Nothing is foolish if you are capable of following the project to the end. Vox AC 15 has vibrato ch which is a big bite for diy. In addition, the chassis is too large, unusable for guitar amp.
If you have decided to diy tube amp, pay attention to AC15H1TV & L schematic

http://dealers.korgusa.com/svcfiles/AC15H1TV&L_SManual.pdf

[trobbins]

Given the 310-0-310 (and assuming the heater voltage is ok for the applied mains ACV that gave 310-0-310), and the 5U4G, you could measure the PT winding resistances, and note the first filter capacitor value, and use PSUD2 to confirm what B+ you could achieve and with what loading, and with what diode options you have. That would put you in a good place to check if another amp is going to suit what you have.

If the OT's were 37:1 for P-P, then a nominal 8kohm PP (based on STC report 6BQ5 pentode mode with 300V plate and screen supplies and common cathode bias for 20W output) would relate to a 5.8 ohm secondary side speaker. If you don't know the original speaker, then that would be a reasonable start assumption which you could then modify for 4 or 8 ohm speaker matching if you wanted.

Are the OPT's on another chassis?

[vintagekiki]

It's monoblock

https://www.usaudiomart.com/details/118556-baldwin_organ_6bq5_el84_mono_block_pull/images/128227/

https://www.canuckaudiomart.com/details/118556-baldwin_organ_6bq5_el84_mono_block_pull/ ¹⁾

[trobbins]

Does that mean its a quad 6BQ5 output stage? The OPT would then likely be circa 4k:3 or 4 ohm.

[vintagekiki]

Yes.
OPT primary is 4k (4x6BQ5 or 2xEL34); secondary any from 4 to 16 ohm

[Pixel]

Given the 310-0-310 (and assuming the heater voltage is ok for the applied mains ACV that gave 310-0-310), and the 5U4G, you could measure the PT winding resistances, and note the first filter capacitor value, and use PSUD2 to confirm what B+ you could achieve and with what loading, and with what diode options you have. That would put you in a good place to check if another amp is going to suit what you have.

If the OT's were 37:1 for P-P, then a nominal 8kohm PP (based on STC report 6BQ5 pentode mode with 300V plate and screen supplies and common cathode bias for 20W output) would relate to a 5.8 ohm secondary side speaker. If you don't know the original speaker, then that would be a reasonable start assumption which you could then modify for 4 or 8 ohm speaker matching if you wanted.

Are the OPT's on another chassis?

One of the OPT was on this chassis, I've got that one and another OPT that was remote. I traced out part of the circuit and can see one pair of 6BQ5 go to the OPT on this chassis and the other pair of 6BQ5 go somewhere out of the chassis along with the B+. I can see where the guy I got this from has written on the OPT 2xEL84.

It is quite interesting to puzzle out what was going on in this amp, it is too bad it already had a few things clipped out when I got it as I'm quite curious about what was going on.

I'll give PSUD2 a shot. The big can cap is 3x40uF 450V, which seems to be consistent with 5U4G.

[Pixel]

Nothing is foolish if you are capable of following the project to the end. Vox AC 15 has vibrato ch which is a big bite for diy. In addition, the chassis is too large, unusable for guitar amp.
If you have decided to diy tube amp, pay attention to AC15H1TV & L schematic

http://dealers.korgusa.com/svcfiles/AC15H1TV&L_SManual.pdf

Since this Baldwin chassis is too big for a guitar amp I am going to postpone doing anything with it and get another chassis and focus on making a Champ amp instead. I have the PT and OT for a Champ amp somewhere, I just don't know where I put them.

If I can find a matching pair of P-P OT then I will probably turn this Baldwin into a stereo amp based on the Tubecad EL84 amp.

[vintagekiki]

If I can find a matching pair of P-P OT then I will probably turn this Baldwin into a stereo amp based on the Tubecad EL84 amp.

That will be your best job.