5E3 Standby?

[Jazz P Bass]

The 1 ohm resistor is for a cathode grounded push/pull amplifier.
Again, this is not what you have.
You already have a cathode resistor in the amp.
Measure the voltage across it.
Divide that reading by the resistance.
Bingo: you now have your current reading.
Ohms Law: I=E/R

[stephenhartley]

5E3 bias

So simple when you explain it - thanks

[Bruce / Mission Amps]

I built a few little 15 watt 6V6, 4x8 amps a while back... fun little bugger. I called them the Bassboy Amps.

[Corona Blue]

My bet is that He was gonna tell you that you don't need one. You really don't. Unless you just want one, then go for it. I have built 5e3s with and without. Doesn't matter. If you do add one, then I'd put in on the OT center tap rather than on the b+.

It's true that you don't need one, but... if you plan on using expensive NOS tubes, there is a benefit to slow warm up and slow cool down of the tubes. They will last longer (all other things remaining the same).

Enjoy the tone!

CB

[stephenhartley]

5E3

I finally found the time to finish my 5E3 project (with a Bruce Collins tone mod) and after stupidly blowing a mains transformer (and replacing it) I switched on for the first time today.

The sound is barely audible at full volume and is very distorted.

The current across the 6V6s is measuring 1mA and it should be 30 to 40.

I've measured the resistors and the 4 68k's in particular are measuring only 34k - some of the others are as much as 20% out - could this be the problem?

Any suggestions would be gratefully appreciated

[Bruce / Mission Amps]

34K could be right as the switching jacks are probably correctly closed with no phone plug inserted.
Can you go through the amp with some simple voltage measurements?
All the positive leads of the three main filter caps, the 6V6s screen voltage (you might have forgot to run the jumper wire from the eyelet board to the screen lugs on the power tube sockets) and on the preamp plates lugs 1 and 6 and their cathodes lugs 3 and 8?

[stephenhartley]

5E3 - hardly any volume

Thanks very much for that advice. I will go through and check.

Instead of the original heater supply circuit, I have fed the heaters in parallel with a pair or 100k resistors running to ground from the pilot light - should lugs 1&2 on the 6v6s still be joined?

[stephenhartley]

All the jumper leads are in place. The voltages on the filter cap +ves from the cathode resistor side read respectively 14, 0, 0 so there's something wrong there

[stephenhartley]

my mistake - I was reading AC oops - the voltages are 364, 266 and 200

[Bruce / Mission Amps]

#1 on the 6V6s is doing nothing (nothing connected to it in the glass envelope) #1 and #2 are not to be connected.
#2 is your filament lug... as is #7. #8 Is connected to #8 of the other tube and then connected to your 5 watt biasing resistor on the board.
Also, I think you'll find that 100 ohms is what you wanted on the pilot lamp assembly.
Your DC voltages on the hi-v caps are not very far off right now either.... keep posting voltages from the preamp etc...

[Tom Phillips]

Re: "...... keep posting voltages..."
What is the screen voltage on the 6V6s?
Measure it right at pin 4 of the tube socket.

Would be nice to see some pictures. Detailed gut shots. Can you do that?

Tom

[stephenhartley]

5E3 voltages

Ok - voltages are as follows:

12AY7: 1: 92v, 2: 0v, 3: 1.4v, 4,5 -H, 6: 96v, 7: 0, 8: 1.4v
12AX7: 1: 130v, 2: 0,3: 1.2v, 4,5 - H, 6: 165V, 7: 18v, 8: 38v

6v6: 3: 365v, 4: 268v, 5: 0.6v, 6: 0.05v
6v6: 3: 357v, 4: 267v, 5: 0.1v, 6: 0,1v

Will try and put some pics up

This is my first foray into amp building - steep learning curve

[stephenhartley]

pics



...... doesn't seem to let me upload pics

[stephenhartley]

oh - it's worked - here's another couple

[stephenhartley]

I'd be very grateful for any suggestions re above voltages.

With inst channel turned up full, volume is very low and distorted. Above half way, the mic channel produces a rhythmic staccato clicking noise.

I've checked the speakers (wired for 4 ohms) and they're fine