SR45 Leds out

[awsjr]

on the "B" side of the board, c4s section...one led is out and the other is dim....I need some help on where to start to figure out what may have caused this... the "A"side leds are bright...thanks

[Paul Joppa]

It was never a full kit, so there is no manual. There must have been some instructions at one time, but I don't have them. Consequently I don't know which C4S is "A" or "B" side.

My guess would be that if there is a problem with the C4S, it will be the one that supplies the shunt regulator. Especially if the power line voltage is greater than 120 volts, that side gets very hot. (Look for darkening of the PC board around the 5731A transistor.) The transistor may be toast - literally!

I do have my original schematic, so you can take voltage measurements at the tube pins and I'll try to interpret them.

[awsjr]

thanks Paul...you are correct that it is the c4s side of the board....bring a variac home tonight and will post some measurement as soon as I can.... it is both amps too so whatever caused the failure did a good job

[Paul Joppa]

thanks Paul...you are correct that it is the c4s side of the board....bring a variac home tonight and will post some measurement as soon as I can.... it is both amps too so whatever caused the failure did a good job

Both amps at the same time? Yes, a power line transient will be the likeliest cause, and dead semiconductors on the C4S boards are the likeliest result. You may want to replace them all.

[awsjr]

hi Paul...good news bad news... the leds light but are dim... I had too much back light to really see them before....
was able to get some readings on the 9 pin socket(s)...
B4 & B5 are within range 3.08, 3.05 vac
B1 314, 314 ... should be 140-210
B3 7.98, 7.95 ... should be 1.56
both B1 & B3 are high according to the Paramour II sheets if those number should be used...any other measurements needed ?...
I will see what you think before going forward.... thanks for your time and happy new year

[Paul Joppa]

The Paramour voltages are not applicable to the SR45.

B tube voltages should be:

pin 1 - 320v
pin 2 - N/C
pin 3 - 8v
pin 4 - 3.15vAC
pin 5 - 3.15vAC
pin 6 - 200v
pin 7 - 0v
pin 8 - 0v
pin 9 - 13.5v

These numbers indicate that both sections are operating properly.

One side of the board - I don't have a record of which, but from your description I am guessing this is the "A" side - should feed the shunt regulator - it will connect to B1, from the middle pin of the MJE5731A, which presumably has a heat sink attached. This section will have brighter LEDs because all of this section runs at much higher current - the LEDs get 5mA, compared to 1mA on the other section.

So, I don't see any problem. Does it work? Does music come out?

[awsjr]

well I had them on the work table to take out the EXO 36 cobalts and put the BH-5's back in....
while I had the chance I thought I would take and look at everything prior to setting them up again...

I will hook them up later today....thank you for providing the proper voltages.... I should have that for the future....
thanks

[awsjr]

Hi Paul.... hooked up and I had no sound from one amp which really was the reason for starting this whole process to begin with... swapped tubes and it followed the tubes.... so I had a dud 6CM7 ....I also saw a thread where you indicated the a 12AT7 could be subbed for the 6CM7.... is this correct ?... are there any changes needed to use this tube.... once again, thank you for your responses and help.... you support is really invaluable.... Happy New Year -Al

[Paul Joppa]

No, I must have been unclear. There is no good substitute for the 6CM7. With a different socket wiring, I think a 6CS7 would work, and with an octal socket the 6DN7. But I have not tried any of these.

[awsjr]

I found the thread Paul that mentioned the 12at7 for the sr 45...

http://www.bottlehead.com/smf/index.php/topic,363.msg6160.html#msg6160

everything is working well now.... thanks again

[Doc B.]

The critical point is the next paragraph after the mention of the 12AT7 -

"Of course, the 12AT7 operating point IS well established for this application... :^)

The shunt reg can be segregated to a single tube as well, possibly an EL-84 or 6V6/6AQ5, triode wired. Those pentodes aren't rated for enough voltage, but a zener between plate and screen will make them triodes with better longevity."

So you would need to add another socket for the additional tube. If you do that, you don't need a dual triode like a 12AT7. You might as well use a 6AB4 with the triode wired 6AQ5.

[2wo]

For what it's worth. I went back to the 6CM7, it's a good sounding tube...John

[awsjr]

you got it John...for how good these amps sound right now I'm not going to change anything... bought 6 Mullard 6Cm7's, are rare find, and swapped out Sylvania labeled "industrial" tubes and have fantastic detail.... not using a pre amp and the gain is enough...