Questions about a recent clubman build.

[turbofeedus]

So I recently built a matchless clubman, working off the schematic attached. Posted in xtian's thread, see there for some build info.
I've updated the voltage chart to reflect my actual amp.

A couple things that are concerning;
1) Why am I dropping ~40Vdc across my choke? The choke measures ~460ohm dc resistance, that's 86mA on B+?
2) My transformer is 300-0-300, not 345-0-345. I assume that's causing some lower than ideal voltages globally. Should I rock it as is, or play with some of the dropper and load resistors?
3) My EL34 are running about 50% dissipation according to robrob's calculator. I have the resistors to sort this out, namely swapping a ~250ohm in for each cathode. Should I mess with this before I sort out the choke-voltage issue, or are they more independent?

Learning as I go, this board is great. Thanks all!
- Joe

[sluckey]

Do you possibly have the OT center tap connected to node B rather than node A?

Using the numbers in your voltage chart and Rob's bias calculator I get 76% plate dissipation for each tube.

[turbofeedus]

Do you possibly have the OT center tap connected to node B rather than node A?

Sluckey to the rescue once again. Thank you.

Using the numbers in your voltage chart and Rob's bias calculator I get 76% plate dissipation for each tube.

Ah, I didn't mention I actually used 470R resistors instead of 330R shown in the schematic. I was trying to correct for matchless running their tubes at ~125% dissipation, but I was ignorant of the lower voltages coming from my transformers compared to the schematic.

EDIT: learning in action, I see now how that's going to affect all the voltages. Glad I got an assortment of 10W cathode resistors!

[turbofeedus]

Here's the current state of affairs on this build.
Updated schematic attached.
Overall Changes:

Changed V1 anode resistor to 100K.
Changed "E" node dropper resistor to 22K.
Changed V2 anode resistor to 220K.
Changed Bass potentiometer to 1M Linear.
Put the 180pf bright cap on a switch.
Changed grid leak resistor after V2 to 470K.
Changed PI to 12AT7.
Changed grid stopper resistors on EL34s to 1.5K.
Changed EL34 cathode resistors to 270 ohm.
Removed 1K/25W pre-screen resistor.
Tube rectifier is 5AR4, not 5U4.

Listen to the amp here:
Soundcloud samples

Mather cabinet came! Picture attached.

I'm not quite happy with the sound of the amp.
It's quite a full sound, the low end is very prominent. When the bright cap is engaged however, the high end can be quite piercing, especially with the bridge pickup on the tele.
Ideally I'd like to reign in the bottom end, and also tame the high end with the bright cap engaged.
Changes I'm thinking:
- decrease the coupling cap after V1 to a 0.01uF.
- put a resistor in series with the bright cap (something like a 220K)
- put in a high value grid stopper on the EF86 (my understanding is this can ease the harsh high end transients, and can be a higher value because the Miller effect is reduced in pentodes?)

I'm also wondering if the increased plate resistor on V1 is loading down the tone circuit in an unexpected way? Matchless used a very small 18K resistor here originally.
Reason being the bass control is still not working how I think it "should". It doesn't seem to do much of anything for the first half of the sweep.

[Colossal]

Hey Turbofeedus,

I've been following this thread with interest. Regarding the Bass control, I believe that pot is supposed to be a 1M reverse audio, so maybe that would explain why you are only getting anything to happen at the end of the rotation (if you are using a log taper). Just a thought.

[turbofeedus]

Hey Turbofeedus,

I've been following this thread with interest. Regarding the Bass control, I believe that pot is supposed to be a 1M reverse audio, so maybe that would explain why you are only getting anything to happen at the end of the rotation (if you are using a log taper). Just a thought.

Yeah so I think the bass control in the layout is designed to use 1M audio and just has the lugs reversed. What I found though is, while the control works as you'd imagine (more bass -> clockwise), it was only the final 30% of the rotation that had any effect. When I changed to the 1M linear (still wired backwards mind you), it "stretched" that range of usable adjustment. Now it starts adding bass around the noon position.

I still think there's something going on with the prior stage's impedance having an effect on the tone circuit. I can't come up with another reason why this would be happening, or why matchless would use a 18K plate resistor on V1.