SP 12 SE

[speakerman1]

By the way 275 volts DC bites like 480 AC. Harder to turn loose of also.

LOL I told you.

Larry

 

[speakerman1]

Turn your gains down. The higher the gain the more noise. You want the least amount possible. I'm learning also. Al least I have a concept of what gain is now. LOL

Larry

This is not your father's SS. LOL

 

[Skratch]

Lee, That is a large amount of gain. Make sure your tube cathode resistors are correct. Do any of the tube plates glow red?

 

[laatsch55]

No they don't Mark. What bothers me the most is when an input is turned off there is still an output for that channel.

 

[laatsch55]

This is not your father's SS. LOL


Amen!!

 

[speakerman1]

Lee
If you are getting output on one channel I would say it has to be at the output selector. Have you tried it in every position? I'm just thinking out load. How else would you get output? Oh great ones please tell me if I am wrong. Could there be bleed through from somewhere else.

Larry

 

[Rex Everything]

.I'm in the process of designing a EL34 amp, with 100w from 2 tubes

I'm still excited to hear about how someone is going to get double the maximum output of a tube from it.

 

[laatsch55]

Larry, it could be from the populating of the input resistors for the MM MC options. Still studying that.

 

[laatsch55]

I have a couple 12ax7's and some 12au7's, could I sub out the 6922's with some of thgese to eliminate the tubes as the source of the problem?

 

[speakerman1]

Don't think so. I could be wrong. Can you just pull the wires
from the board and see what happens. Thus taking the phono out of loop?
larry

 

[laatsch55]

Larry it's isolated to the phono board ONLY. When the selector is moved to any other input all the above behaviour stops. The rest is golden.

 

[laatsch55]

Here's the schematic. C2 is now a 100 volt 100uf electrolytic. The original parts list shows a 47uf at 25 volts. Could this be the source of the excessive gain??

 

[soundude]

Hi Lee sorry, been working my ass off this past week, installed new air handler and of course everything went wrong....got 30hrs overtime though...Yehhh!
Anyway check the resistors in the circuit to make sure they are closely matched, then check the selector switch to make sure the contacts make solid and the check the potentiometer is balanced through the entire rotation...if all that is good the tubes triodes are not balanced...6dj8 is the only replacement tube and it is a frame grid tube and high transconductance...there really is no replacement tube for that. alterations of the circuit and pinout changes a 12ax7 can be used but at the cost of gain. personally I dont like 6dj8, easy to pickup noise because of the high gain. A nice pentode phono stage gives you more versitility and sonics with a wide range. That schematic looks like a copied counterpoint circuit. Anyway most likely unbalanced tube or volume pot...I can see if I have some 6dj8s in my arsenal...

 

[soundude]

Hey Larry, Getting power from a pair of tubes isn't to hard, unlike transistors tubes have a many setups and parameters that make them very versital. So I will explain, the nice thing about the EL34 or 6ca7 is the operating voltage range is extremely broad...250v to 800v.

Class Va Vg2 Vg1 Ia Ig2 Ra S Rk Zout Pout THD Notes
AB1P/P 775 400 -39 50 - 182 6.0 - 38.0 11,000 100 5 Shared Rg2 = 750 ohms

Very close to the max operating currents but with the higher voltage the power output is obtainable. Tubes won't last that long but with the right tube you can get a good 5 to 8 years at these parameters. If you go NOS mullards or Philips you can get over ten years since they used better materials.
Front end is a pentode/triode configeration, good 6U8 would work great here, awesome range and sonics of a pentode so early in the stage will enhance the range at the output..
Its also very easy to get 100watts from a pair of 6550s or kt88s and another great tube the 6146s, with this same theory...These tubes would live a longer life since they have better plate ratings than the EL34.

 

[speakerman1]

It better not be a pot. I would be very upset. I may even swear a little.

Larry

 

[soundude]

Format I setup for the ratings didn't stick when posted, but you should figure out the lineup.

 

[soundude]

Larry, accually constructed amp already but my friend liked it so much he took it to try it and I don't think he has intentions of giving it back...
I will scan circuit and post later..
I was planning on building the old Mullard circuit with 10 kt88's for 400w output but need to get a 1.2k output wound, calculating it will be 35lbs per tanny...WOW, won't have to go to gym that week....LOL.

 

[speakerman1]

Pots are gold point. Lee checked them. They were .005 to the resistance. The volume control is a TKD.

Larry

 

[speakerman1]

My Carys weigh I think 75 lbs each. I hate to pick them up.

Larry

 

[soundude]

I here ya those tube amps keep us fit..., looked in my stash haven't found any 6dj8s..goin to have to go in the cold storage dungen to see if I have any in archive...