5E3 plate voltages too low?

[markmalin]

Hello all!


I just finished a 5E3 build using spare parts I had in the shop.  My goal is to use it as a "mule" to experiment with adding a 1-tube reverb and some other tweaks.  I followed Hoffman's 5E3 circuit.  It sounds "ok", but I noticed the plate voltages are pretty low.  My question is, are these too low? 


I had a spare Mercury FBFS-P40X transformer rated 325-0-325.  I'm only seeing about 303V on the 6V6 plates, though.  Here are the other tubes:


12AY7
V1a  103V
V1b  102V


12AX 7
V2a  123V 
V2b  157V


6V6 plates  303V


The bias voltage on the output tubes is only at 16V


Again, it sounds ok, but wondering if this is too low, especially on the Power tubes.  I don't have the $ for a different transformer just now, so using this one was a no brainer.  FWIW the OT was also a spare MM Radiospares 045RS-L and I'm using the 8K primary.


Thanks for any thoughts on this.

Incidentally...I had accidentally put the 12AX7 in V1 and the AY7 in V2 and it had lots of sweet bite to it.  :)

[markmalin]

here's another pic.

[John]

Try another rect. tube? Maybe only half of it's "working". You should be getting over 400 coming  at the OT CT if I'm thinking right.

[markmalin]

Try another rect. tube? Maybe only half of it's "working". You should be getting over 400 coming  at the OT CT if I'm thinking right.

I'll give it a try.  I've got a solid state plug in I can try. 

[eleventeen]

Your 325-0-325 tranny should produce 1.4 * 325 = 455 minus 50 or 60 volts across a 5Y3 or 5U4. A GZ34 should drop about 25 volts. Either way you should have much closer 400 volts on your B+ as I figure it.
 

[markmalin]

That was it.  Bad rectifier.  Interesting...I've never seen that before.  I installed a Yellowjacket 5E3 solid state plug in and now am seeing:

12AY7
V1a  135.7 VDC
V1b  135.7 VDC

12AX7
V2a  170 VDC
V2b  217 VDC

6V6 plates:  425 VDC
 
power tube cathode bias voltage 23 VDC


Cool thing is, I called CE Dist and they're sending me a new JJ and don't need me to return this one :)


Thanks for the help, guys!
Mark.

[sluckey]

I like your other voltages better! With that yellow jacket your 6V6s are idling at 18.5W. That's very hot. 6V6 is a 14W tube. Take a look at my voltage readings in the pdf below...

BTW, I'm using a PT from a Reissue Deluxe Reverb. It put out 330-0-330VAC that made 420VDC B+ in my Deluxe Reverb with power tubes idling at 24mA/tube and a 5AR4 rectifier. Same transformer only made 340VDC B+ in my 5E3 idling at 36ma/tube and a NOS 5Y3.

     http://sluckeyamps.com/5e3/5e3.pdf

[dude]

I thought the standard 5E3 uses a 5Y3, American old stock as the Russians ones produce a higher B+.

Usually, I think with the 325-0-325 PT you'd see about 345v to to 365V  at the plates with the 5Y3 and a 250ohm cathode bias resistor.

At least that's what I got from the one I build, just pretty much stock vintage specs.

Change to 6L6's with a little bigger OT and a few changes in the dropping resistors and you got Neil Young's amp.

Al

[markmalin]

I got the new rectifier and installed it.  345V at the plates.  I'm much happier with that!  Must have been a bad tube.  At least CE Dist swapped it out no hassle...