First off I would like to say.... great board! I have been reading and learning and developing a great respect and appreciation for all of you out there! and now the time has come for me to ask for HELP/Advice. I recently decided to re-build my trusty rusty old ST-70 after the quad cap finally went. In my search for parts and information I discovered your nice friendly place here (had I found it a day sooner... I would have gotten the VTA driver board).
I used the stock transformers, the Dynakitparts 80,40,30,20 Quad cap, as well as their Bias update kit, and I used the Triode electronics ef86 driver board.
After rebuilding I first shorted the inputs, and hooked up some old POS speakers and powered it up with no tubes at all... nothing exciting happened so following directions from Triode I plugged in my new 5AR4 (only the 5AR4) and when none of the magic smoke was released...... I proceeded to check voltages on the driver tube sockets (I don't know if anyone knows much about this board here or not but I will present my findings so you all will understand my concern)
2 EF86 Sockets:
pin 1 Screen, should be 55-80V, is 373V
pin 3 Cathode, should be 1.2 - 1.6V, is .96
pin 6 Plate, should be 80 - 110V, is 418V
1 12AU7 Socket
pin 1 Plate 1, should be 235 - 265V, is 478V
pin 2 Grid 1, should be 80 - 110V, is 416V
pin 3 Cathode 1, should be 90 - 120V, is 0
the second half of the tube reads the same numbers
Hmmmm I say, those look a tad high! I got my handy dandy color chart out and checked placement and value of each component on the board, All is as it should be, I also re-confirmed all hook-ups on the board, all is as it should be. (I will write and ask Triode's Tech support after I finish here).
So, I fired it up again and checked all the Dynaco test points (heres where I think you all can help) I don't know if these numbers are supposed to be checked with or with out tubes in but here is what I find with only the 5AR4 in:
EL34 Sockets (consistant on all 4 sockets):
pin 2 6.3
pin 3 500V
pin 4 500V
pin 5 -47Vac
pin 6 -47Vac
pin 7 6.3
5AR4:
pin 2 504V
pin 4 367Vac
pin 6 365Vac
pin 8 501
Quad Cap (as per Dynakit parts , this cap is installed 1/4 turn counter clock wise from the original with the 80 lug facing the back of the amp but I used the original Dynaco lug/location numbers for this check, not the symbols) :
lug 3 422V
lug 4 476V
lug 1 492V
lug 2 494V
Selenium Rectifier (now a diode)
+ 52Vac
- -70Vdc
Circuit board eyelets 3 and 18
478V
Now with no load on it and the old PTX on modern line voltage hmmm I can see 20% hotter numbers, but the driver board... WoW!!
any thoughts, suggestions? (other than "Yo! don't put any tubes in that thing!!" lol) but seriously any help would be greatly appreciated!
Thanks one and all!
The New guy
Will
I used the stock transformers, the Dynakitparts 80,40,30,20 Quad cap, as well as their Bias update kit, and I used the Triode electronics ef86 driver board.
After rebuilding I first shorted the inputs, and hooked up some old POS speakers and powered it up with no tubes at all... nothing exciting happened so following directions from Triode I plugged in my new 5AR4 (only the 5AR4) and when none of the magic smoke was released...... I proceeded to check voltages on the driver tube sockets (I don't know if anyone knows much about this board here or not but I will present my findings so you all will understand my concern)
2 EF86 Sockets:
pin 1 Screen, should be 55-80V, is 373V
pin 3 Cathode, should be 1.2 - 1.6V, is .96
pin 6 Plate, should be 80 - 110V, is 418V
1 12AU7 Socket
pin 1 Plate 1, should be 235 - 265V, is 478V
pin 2 Grid 1, should be 80 - 110V, is 416V
pin 3 Cathode 1, should be 90 - 120V, is 0
the second half of the tube reads the same numbers
Hmmmm I say, those look a tad high! I got my handy dandy color chart out and checked placement and value of each component on the board, All is as it should be, I also re-confirmed all hook-ups on the board, all is as it should be. (I will write and ask Triode's Tech support after I finish here).
So, I fired it up again and checked all the Dynaco test points (heres where I think you all can help) I don't know if these numbers are supposed to be checked with or with out tubes in but here is what I find with only the 5AR4 in:
EL34 Sockets (consistant on all 4 sockets):
pin 2 6.3
pin 3 500V
pin 4 500V
pin 5 -47Vac
pin 6 -47Vac
pin 7 6.3
5AR4:
pin 2 504V
pin 4 367Vac
pin 6 365Vac
pin 8 501
Quad Cap (as per Dynakit parts , this cap is installed 1/4 turn counter clock wise from the original with the 80 lug facing the back of the amp but I used the original Dynaco lug/location numbers for this check, not the symbols) :
lug 3 422V
lug 4 476V
lug 1 492V
lug 2 494V
Selenium Rectifier (now a diode)
+ 52Vac
- -70Vdc
Circuit board eyelets 3 and 18
478V
Now with no load on it and the old PTX on modern line voltage hmmm I can see 20% hotter numbers, but the driver board... WoW!!
any thoughts, suggestions? (other than "Yo! don't put any tubes in that thing!!" lol) but seriously any help would be greatly appreciated!
Thanks one and all!
The New guy
Will