New amp build transformer suggestions

[Bonsaimaster]

Dear colleagues,

I am looking to build a Bad Cat Hot Cat amp. The schematic is included. Instead of making a dual EL34 version I want to downsize this to a single EL34 tube. I am looking for how to calculate the PT and OT and choke for this configuration. I have what I think are the original specs for the full version. Any help would be appreciated.

*575 volt ac ct 600 ma************285-0-285 250MA
* * *6.3 volt 6 amps***************5.0 Volt 3 Amps
* * *5.0 volt 5 amps***************6.3 Volt 6 Amps

30 watt Choke: T541690
* * * Inductance 36 Henries

30 Watt Output: T541691 Cutout 1¾” x 2¼”
* * *Primary Impedance 4000 ohms
* * *Secondary Impedance 4,18,16 ohms


Thanks in advance,

Daniel

[eschertron]

Welcome to the forum, Daniel!

* * *6.3 volt 6 amps***************5.0 Volt 3 Amps
* * *5.0 volt 5 amps***************6.3 Volt 6 Amps

Not sure what this means. How many filament windings are there on the PT? Also, the schem linked does not come up. There was a server crash a few years ago that corrupted the links.

But in general answer to your question, turning a push-pull amp into a single-ended amp will require some design changes to the power amp section - mostly the phase splitter circuit - and a downgrade to the power supply. Then the gain throughout the amp will need to be checked and massaged to see how it compares to the original design. Why not find a SE EL34 circuit out there to build, try it and then see what could make it more like the bad cat. I'm not familiar with the bad cat, but I'll hazard a guess and say the preamp is similar to many Fender and early Marshall designs.

[Roberto]

This is the schematic: http://schems.com/bmampscom/badcat/badcat_hotcat_30.pdf
I'd go from V1b to V3b with another 470k à la Marshall 1959.
Then from F to the Power tube.

As for the PT, please specify what do you have actually, as per the information shown on my link, voltages are different.

Thanks.

[Bonsaimaster]

This is the schematic: http://schems.com/bmampscom/badcat/badcat_hotcat_30.pdf
I'd go from V1b to V3b with another 470k à la Marshall 1959.
Then from F to the Power tube.

As for the PT, please specify what do you have actually, as per the information shown on my link, voltages are different.

Thanks.

Ok I feel like an idiot. I Thought this was a SE design but realize it is a cathode bias PP amp. Ok I am using this transformer (320-0-320) at 150mA center tapped, 6.3V (3.15-0-3.15) at 4A center tapped and 5V at 2A.

Ok I think best to keep the PP design. So the question is which output transformer to use? I have two Classic Tone transformers
40-18049
40-18006
40-18080 Hi Fi version

The first two have the same specs but different in size. So there must be something else going on.

Also do I need a 36H choke? I would like to use a 30H one.

Thanks
Bonsaimaster

[Roberto]

Hi Bonsaimaster,

Do tou have the direct links or specs of the cited OTs?
Just to tell you which one fits better the actual configuration.

You'd like to use one single SE to reduce the power?
you could choose a EL84 PP instead.
Around 8k Raa.

[Bonsaimaster]

Hi Bonsaimaster,

Do tou have the direct links or specs of the cited OTs?
Just to tell you which one fits better the actual configuration.

You'd like to use one single SE to reduce the power?
you could choose a EL84 PP instead.
Around 8k Raa.

I think I will stay with the EL34 PP
40-18080
Vox AC 30 Vintage Style Output Transformer, 4/8/16 Ohm
Fender Output Transformer, Bandmaster, Pro, Vibrolux, Tremolux, Vibroverb, 4/8/16 Ohm

Thanks!

[Roberto]

If you want to do some trials on the sound and not an exact replica, you can chose the first OT: it has 4.4 and 6.6k taps plus the UL ones. Many switchable options.

Otherwise the other two seems quite similar (but I don't have direct experience on them).