5x3 DC voltage on pin 5

[strat100]

Just built a home brew 5x3 cathode bias and hammond trannies,and on measuring voltages on first start up i am getting dc voltage on both pin 5's of the jj 6v6,here are the voltages throughout the amp =

12ay7
pin 1=150v
pin 2=0v
pin3=2.42v
pin 6=148.6v
pin 7=22.2 mv
pin 8=2.42 v

12ax7
pin 1=195v
pin 2=0v
pin 3=1.51v
pin 6=232v
pin 7=26.65v
pin 8=66.8v

6v6 v3
pin 3=443v
pin 4=410v
pin 5=40mv
pin 8=31.65v

6v6 v4
pin 3=440
pin 4=409v
pin 5=77mv
pin 8=31.6v

gz30
pin 2 and 8=5.09ac
pin 4=160v
pin 6=160v
pin 8=440v

voltage across 469r resistor is 30.75v which gives about 13w and i think its in the ballpark for jj 6v6.

havnt plugged guitar in yet but have a dummy load attached and a little scared as only built a couple of kits before and this is my first homebrew,i am thinking i am going to have to bring the voltages down and try and use a 300r resistor i have waiting.but will wait for advice from you guys before i proceed.

[eschertron]

Whats the pri Z on the output tranny? With 8ka-a the model I plugged your values into looked pretty good. A solid 100% dissipation at idle, max dissipation at around 16W, but that's what I've seen with my 6V6 tubes. And an output transfer curve straight as an arrow. Hope you're looking for loud and clean!

[strat100]

Thanks for the reply.

Output tranny is a hammond 1760j at 4000k.
Loud and clean isnt exactly what i am looking for ,so whats the best way to address the loud and clean?

[eschertron]

Thanks for the reply.

Output tranny is a hammond 1760j at 4000k.
Loud and clean isnt exactly what i am looking for ,so whats the best way to address the loud and clean?

At 4000 anode-anode you might be in meltdown territory for 6V6s. Just a thought: Why not put in 6L6s, since that's the direction the OT seems to be going?

There are plenty other options though. don't get discouraged by what I've said. Things I've seen suggested on this forum include:
Recto tube that drops more voltage (lowers B+ and everything else) or D@MN BIG resistor in front of B+ node
bigger resistor before screens to help control dissipation (I'll have to look at that to see how it affects the tube operating curve)
other solutions are more esoteric, like a variac in front of the amp to bring line voltage down to 'vintage' levels

[strat100]

Thanks eschertron food for thought definately,got an nos 5y3 and some zeners on the way so will see what happens when i give them a try and have a good think on the 6l6's after getting the amp in good order.

[g1]

At 4000 anode-anode you might be in meltdown territory for 6V6s. Just a thought: Why not put in 6L6s, since that's the direction the OT seems to be going?

How about doubling the load impedance to reflect back double the primary Z (so 8K).

[strat100]

Thanks G-one but as a relative newcomer who has probably chosen the wrong transformers and has no idea how to double the load impedance, maybe it would be best to put some 6l6's in as the tranny no doubt is best for them or change the output tranny to a deluxe reverb one.

[Justin Thomas]

I think he meant double your speaker impedance? Just a quick&dirty way of using something you might already have on hand... unless you already have a 16ohm in it.

??? :P

Justin

[strat100]

ot has 4,8 and 16 ohm taps and have the 8ohm speaker into the 4 ohm tap

[g1]

have the 8ohm speaker into the 4 ohm tap

That's what I meant. You have doubled the load impedance for the tap. Having a 16ohm speaker on the 8 ohm tap would have the same effect.
So you will reflect back double the specified primary impedance. If the transformer is spec'd as 4K, the way you now have it loaded makes it effectively 8K.
So you seem to be covered as far as the impedance issue goes, but you still have to contend with the B+ issues. If you are too high for the 6V6's you will need to decrease B+ or consider switching to 6L6.
The reason I was trying to avoid the 6L6 is that you said you were not interested in loud and clean, so the 6V6 are probably more of what you are looking for sound wise.

[strat100]

fired her up tonight with a borrowed nos 5y3 which brought the B+ down to 404 but still with a 470 ohm resistor,so still need to address the B+ but the amp was very loud and very clean all the way to 12,luckily no problems with noise infact extremely quiet so i am very pleased and cant wait to lower the B+ and get some grind .

[strat100]

Just an update;added some zeners to the ct and brought the B+ down to 361v and put a 300 ohm on the cathode and that put me at 12.4 watts and the amp has some break up now,not as much as expected but that could be down to the cannabis rex speaker,thinking of getting a jensen jet lightning to see if that helps.

[eschertron]

Are you using a 12AY7 in the V1 position (indicated in post #1)? Drop in a 12AX7 to see what the amp sounds like with the output tubes slammed