50w OTS HRM voltage help please

[LPSGME]

I also had (and still do have) a problem lowering my Ceriatone voltages which seem way high.

The original string was 3.3K; 22K; 2.2K; and 220K

I drastically raised the 3.3K like you did, and that seemed too bring everything down.

But last night I decided to take another shot at things and was surprised to find that the voltages were all screwy - particularly V1. V1a was 185v and V1b was 236v. (?????!!!!!!)

I tried changing tubes and even changed the resistors and caps. But nothing fixed it.

I ultimately ended up trying:
2.2k; 22K; 2.2K; and 135K.
That generated:
V1a @ 186V (Vintage RCA)
V1b @ 236V
V2a @ 208V (JJ)
V2b @ 209V
PI @ 315V (JJ)

In order to raise V1a, I decided to just use the supply from V2 - which resulted in raising V1a to 190 and leaving everything else the same.

As I heard a distinct tonal difference, depending on whether I used 2.2K or 3.3k as the first resistor - I installed a switch so I could have either.

I also added 50K pot in series with the 4.7k transformer feedback; and and a relay to auto switch the 150K slope to 100K in OD mode.

I still don't know what happened to make V1b so high. I'm wondering if it could be something with the socket.

But whatever the cause is, the amp has never sounded better.

[markusw]

Just measured:
6.7, 18.5 and 6.2
This yields some pretty low voltages vs.typical, but they seem to work pretty well for me. I have V1=180, V2=192, V3=269. I don't recommend trying my values as your taste, tube type and playing style will likely point towards different targets. This gives a more compressed sound than typical and that seems to work well with my arguably poor right hand technique. Higher voltages had more ping but were less forgiving. Tweeking to your sweet spot is the trick. I still have much to learn in playing and tweeking!

Thanks for posting your dropping string values! Would be cool to have some 2W trim pots....
BTW, I ended up with voltages even a bit lower for V1 and V2 on my Non-HRM build with 2k2/22k/2k2 values with two 60s Philips 12ax7 tubes.
When I used EH or JJ tubes voltages were at least 10V higher.

Here's a list of voltages I took with different tubes in V1 (220k/150k plate resistors):

Philips A: 173/181
Philips B: 175/188
Philips C: 173/180
JJ: 191/193
TAD 7025S RT011: 178/193
TAD 7025 RT10: 191/199
TAD 7025/E83CC: 173/193

I was thinking to add test jacks for V1 and V2 plate voltages. Do you guys think it would introduce a lot of noise even if they are mounted close to the sockets?

[rogb]

I ultimately ended up trying:
2.2k; 22K; 2.2K; and 135K.
That generated:
V1a @ 186V (Vintage RCA)
V1b @ 236V
V2a @ 208V (JJ)
V2b @ 209V
PI @ 315V (JJ)

Interesting results guys, plenty of food for thought here. With regards to the PI, is not 315v on the high side? Still if it's sounding good...
I've got mine at (ISTR) 292/298, the bloom and sustain is very good with this 6v differential, rather than aiming for a perfect balance. Got that tip from here too

[odourboy]

I also had (and still do have) a problem lowering my Ceriatone voltages which seem way high.

The original string was 3.3K; 22K; 2.2K; and 220K

I drastically raised the 3.3K like you did, and that seemed too bring everything down.

But last night I decided to take another shot at things and was surprised to find that the voltages were all screwy - particularly V1. V1a was 185v and V1b was 236v. (?????!!!!!!)

I tried changing tubes and even changed the resistors and caps. But nothing fixed it.

I ultimately ended up trying:
2.2k; 22K; 2.2K; and 135K.
That generated:
V1a @ 186V (Vintage RCA)
V1b @ 236V
V2a @ 208V (JJ)
V2b @ 209V
PI @ 315V (JJ)

In order to raise V1a, I decided to just use the supply from V2 - which resulted in raising V1a to 190 and leaving everything else the same.

As I heard a distinct tonal difference, depending on whether I used 2.2K or 3.3k as the first resistor - I installed a switch so I could have either.

I also added 50K pot in series with the 4.7k transformer feedback; and and a relay to auto switch the 150K slope to 100K in OD mode.

I still don't know what happened to make V1b so high. I'm wondering if it could be something with the socket.

But whatever the cause is, the amp has never sounded better.

That V1b is definitely out of whack. I would suggest the wrong value cathode or plate resistor sneaked in there. What's the cathode voltage on V1b?

[Structo]

The V1b voltage could also be entirely the tube.
Two triodes, one out of balance with the other.

I have noticed this before when rolling tubes through the preamp.
Some tubes will be within 5v while others can vary by quite a bit.

[LPSGME]

I tried 6 different tubes (a few JJ several vintage RCA) and, with all, V1b still read 45 volts higher then V1a. I also changed the plate resistor and cathode resistor and cap on V1B.

I think the cathode voltage is reading 1.35 on V1a and 1.85 on V1b.

The really odd thing is that the voltages were all fairly well balanced before.

The other odd thing is that, 'sometimes', when I put my meter probe on V2b I get a high pitched squeal and the voltage reads very low 160-180 range. But then it changes and goes back to 206 or so. I re-soldered all the the connections, but that make no difference

Before this tube imbalance occurred, I had raised the first resistor (3.3K) in order to lower all the voltages and got V1@185; V2@204; PI@312

But after discovering the imbalance and going back to 3.3K (or 2.2k); 22K; 2.2k and lowered the 230K to 135K - the sound got much better, even though the PI voltage was relatively high and V1 imbalanced.

Being that I hear nothing unusual when playing and the amp sounds sounds better than ever (by 30%), I'm taking the Zen approach.