its been 6 yrs and i finally am getting my build fired up!

[skyripper2]

Thanks Tony. i will have to wait a bit on it as the only 24k i have is a huge one (maybe 5watter)
its big Lol. I will check my local and see what i can find. Little by little it all comes together.

[talbany]

Thanks Tony. i will have to wait a bit on it as the only 24k i have is a huge one (maybe 5watter)
its big Lol. I will check my local and see what i can find. Little by little it all comes together.

You got it!.I am pretty sure that should get you squared away.

Good Luck!
T

[skyripper2]

so changing out the 24 ohm to a 24 k has brought my Pi up to 243volts now . I am thinking the 3k3 needs to be a 2k2 and would get my PI up to the 300v. I also think the resistors 3k3 and 22k are too small a size(the ones i have in it now) and i have bigger ones to stick in (a 2watt and a 3watt)
Good morning .and what say you guys?

[martin manning]

If you still have 400V on the PI supply node you should have about 300V on the PI plates. Something still doesn’t seem right. What values are the V1and V2 plate loads, i.e. is this a high plate or a low plate?

[skyripper2]

i have 150k and 220k on both v1 and v2 .it's a high plate . v1=180v v2=187v v3=243v these are my current voltages on pin 6.
v4 - v7 are 430v on pin 3 and pin 6. PI node has 403v
thanks for the help.

[talbany]

At 400V I get between 260-270 about a 140V drop (Depending on the tube) Try rolling a few in there.
If your going to use Dumbles dropping string values you then go by the Twin PT voltages (450V-460V) so your already sitting about 20 V below that at 430V.So your amp everything will automatically be 20V below spec! using his string on a high plate with the FET
You can try the 2k2 but I doubt you will be able to hit 300V mark with that transformer.

[erwin_ve]

i have 150k and 220k on both v1 and v2 .it's a high plate . v1=180v v2=187v v3=243v these are my current voltages on pin 6.
v4 - v7 are 430v on pin 3 and pin 6. PI node has 403v
thanks for the help.

Can you mention your voltages for both triodes at V1 and V2: so pin 1 and 6 on both V1 and V2?
Can you specify your cathode setup at V3 with voltages? It's still unclear what you actually have in your amp at that point.

[martin manning]

If your going to use Dumbles dropping string values you then go by the Twin PT voltages (450V-460V) so your already sitting about 20 V below that at 430V.So your amp everything will automatically be 20V below spec! You can try the 2k2 but I doubt you will be able to hit 300V mark with that transformer.

The voltage differences will be closer to the same percentage as the B+ change throughout, so 430/450, or 5% low. I agree 2k2 vs. 3k3 will only be 5-6V at the PI plates. Try swapping the tube. I think with 400V on the PI node an on-spec 12AX7 should be 280+.

[skyripper2]

Joy.................
I swapped out the PI tube for another and wouldn't you know it......
i had to bring the bias down afterwards as one tube was at 50mvdc
i now have v1=179v v2=183.8v v3=280v on pin 6. and v1=182v v2=182v v3=281v on pin1
my bias is set at the points as follows v4=37.8 v5=35.6 v6=37 v7=41.1mvdc
I just finished playing it for the last hour and am feeling really good about how it's sounding.
you Guys All Rock. Thank you All so much for the help.

[martin manning]

Great! Now, you might want to swap V5 and V7 to balance the current on each side a little better.

[skyripper2]

Thanks again Martin
I did swap those 2 tubes to see if it made a change, but no change . the values stayed the same.
so for now i am just gonna play the amp and enjoy .

[martin manning]

Just to be clear, the current through those individual tubes won’t change, but the total current through each side of the OT will be closer.

[skyripper2]

understood and true . I'm just very happy to have been lucky enough to have seen this through. For a first build I can only say I have learned a lot and am very greatful to now own an amp like this. Much love to All.
sound clips coming for xmas.

[martin manning]

Cheers! A complex circuit like this is an ambitious undertaking for a first amp project, but you probably knew that already ;^)

[talbany]

Joy.................
I swapped out the PI tube for another and wouldn't you know it......
i had to bring the bias down afterwards as one tube was at 50mvdc
i now have v1=179v v2=183.8v v3=280v on pin 6. and v1=182v v2=182v v3=281v on pin1
my bias is set at the points as follows v4=37.8 v5=35.6 v6=37 v7=41.1mvdc
I just finished playing it for the last hour and am feeling really good about how it's sounding.
you Guys All Rock. Thank you All so much for the help.

IMO it's not that uncommon to get wild voltage swings on the PI.I find many of the vintage tubes draw more current and read a bit lower than new production, especially if the vintage ones have been used and abused! This is why I always buy tubes that have been tested and matched when I get my new ones, IMO well worth the added cost and time rolling through tubes.Glad you got it sorted out and looking forward to some clips!!

BTW.Like Martin says! Try to get a better balanced tube in there!. Bring it up to Dumble Specs!

Tony