Tube power transformer wires

[s0b9r]

True, I had no capacitor on. That's the peak voltage opposed to rms right?

About the current limiter, I'll be using the schematic from this video https://www.youtube.com/watch?v=wRFRwOnLsZI  amazing channel by the way..
  is this correct?

Next, I'd like to figure out the output transformer:


Once again, the wiring is not clear. Any ideas about how to work on this one? Also since it'll be a single ended amp, this transformer is ok right?

Thanks again for your help and excuse my question bombing!

[PRR]

> the output transformer

OTs are usually something like 5K:8r. The DC (ohm meter) readings tend to be about 1/10th of the nominal audio impedance. So one winding will show hundreds of ohms, the other will show near 1 Ohm.

I strongly suspect that is a push-pull OT. (Too many leads.) This will not work good in a SE amp.

You have NO notes or data about what these irons came out of? Mystery iron and an inexperienced builder can be a real up-hill project.

[pdavis68]

Tube amp transformers generally follow some similar color codes.

Blacks are generally your primary.

Reds are your high voltage and a red/yellow is usually the center tap for that.
Greens are usually your 6.3V filament taps.
Yellows are usually your 5V filament taps (for a 5V rectifier tube)

This one clearly has multiple primary voltage taps, so those you'll have to determine based on the relative resistance.

Also, the EZ80 uses a 6.3V filament, but according to the schematic, one of the sets of 6.3V leads is going to the rectifier alone and the other to the lamps & filaments for the other tubes. So you'll probably have 2x6.3V taps. The green pair is probably the one that goes to everything but the rectifier. This is important, because it will have a higher rating than the pair going to the rectifier.

Since the radio was running a single ended EL84, you're pretty well set for a nice little practice amp. I built an Epiphone Valve Jr as my first amp. It uses one 12AX7 pre-amp tube and 1 EL84. It's really easy to build.

If you google "SE EL84 guitar amp", you'll find a lot of custom designs people have come up with as well.

[s0b9r]

Ok, here are some updates:

I can also use the transformers from my broken Bugera v22 head. I think it's beyond repair unfortunately, because of the complicated smd board and lack of complete schematic. I talked to a tech and he didn't sound at all promising for fixing it.
So, a push pull output transformer and a more standard power tranformer are now available. Here's the v22 main amp schematic:


It's also possible now to build a more flexible-powerfull amp, so I'd really like to build something like a Bassman but use the el84's that I already have for a power amp stage.
I've found this schematic for a bassman micro:


How possible do you think it is to modify this Micro's output stage for el84s? Maybe at around 20 watts?

[amptramp]

20 watts out of an EL84 is a bit much.  They can do 17 watts for a moderate time or 14 watts forever and their ratings are given for 17 watts at 300 volts on the plate or 11 watts for 250 volts on the plate.  You have to have a grid-to-grid swing of 22.8 volts for 11 watts or 28.6 volts for 17 watts.  The Bassman Micro might be able to drive it but you may have to get a beefier phase splitter than a 12AX7 to supply this drive and at least 30 volts at the 12AX7 grid.  Not that likely with the tone stack in front of it.

Even if the semiconductor logic is not operational, it is not that necessary unless you do your pedal switching at the amplifier rather than the stompbox.  You have an effect module connector that is not that necessary, so its switching circuitry can be disconnected with everything coming in via either input and no footswitch connection at the amplifier.  The Bugera V22 should still be usable.

[PRR]

Use the *real* 5F6a plan input through driver, then use the Bugera's power stage. You are just replacing the 6L6/5881 stage with EL84, and associated connections and bias.

Because the EL84 is higher gain, it will overdrive a bit easier, but that can be OK.

Power output will be just the same as the Bugera; you are not changing PT OT or power bottles. The Bugera (any decent preamp/driver) can slam the power bottles to the max, you get what you got.

That "Micro"s plan has such a poor driver that I can only picture it as a bedroom level preamp-distortion thing, sorta a super-pedal that "can" drive a speaker. A half-pint, instead of the half-gallon a "EL84 Bassman" should be.

[s0b9r]

That sounds better yes! Ok, I tried to combine the two sections:


It's the Bassman preamp up to the tonestack, then the bugera's final gain stage -> phase inverter and then the power amp. I removed the fx loop which I never used anyway.
The power supply is a bit different in the Bugera, as it has a full wave bridge rectifier and no center tap. The point where the two lower diodes' anodes meet goes to chassis ground correct? 
I also removed the 15v regulator etc. Again, they did some things differently, they feed the heaters with 18v dc instead of the 6.3v ac. I've read that maybe there's less noise this way. Is it worth it you think or maybe I should simply use the 6.3v winding for all the tube heaters?

[amptramp]

There are a number of high fidelity receivers and amplifiers that use a DC supply for the heaters.  I have an H. H. Scott 340B receiver that has a separate diode bridge and 48 volt supply to supply the preamp and tone control stages (four 12AX7 heaters in series) and the hum level is quite low because it also generates the fixed bias for the 7591 output tubes.  The other receiver I have does something a little more strange.  It has four EL84/6BQ5 output tubes and the cathodes are all connected together and cathode biased.  Part of the cathode bias load is the heaters for the two 12AX7 preamp tubes.  DC on the heaters will always have some buzz due to frequencies added by rectification but the end result should still be better than AC.

Another stunt you will often see used to keep heater hum out of the circuit is to raise the heaters to a positive voltage.  If the heaters are at a negative voltage, they will emit electrons that may join the electron stream above and below the mica spacers in the tube and this will be modulated by the AC voltage.  By making the heaters positive, the grid will intercept and stop these stray electrons from getting to the plate tabs above and below the spacers.

[s0b9r]

Ι settled on using the Bugera's method for the preamp heaters. They connect all the 12ax7 heaters in series with inly the middle one center tapped if I'm not mistaken.
Here's a layout I made last night:


It's all according to the schematic I posted before. I removed the low input from each channel also don't mind that fuse floating there haha.
If anyone has the patience to check it out that'd be great.

Thanks again everyone for your advice!