Beiträge von gaul

UPDATE: Klaus sent me another OT, with lug 13 connected properly, now the amp works perfectly and the bias can be set in the proper way: just 3mV of difference between Power Tubes...

I want to ask a question without opening a new topic: wich is the specific function of the 4 12AX7 tubes?

I'll try to ask in a simple way:

V1 should pilot the clean channel,

V2 should pilot the channel 2,

V3 should be related to buffered FX Loop

V4 should have something to do with the phase inverter... is it right?

So the question is: If I want to replace the pre tubes: do I have to buy a matched quartet or not?

Thanks to all!

No answer...

Nothing? No one answer?

Please Martin, we need to get a last answer about it: First you said that A15MK2 needs NO additional document, then "Regarding the wiring I will create a new document soon"...

So, surely I'm a little bit stupid but: If someone build an A15MK2 with the actual documentation and the actual wiring for the OT, is doing a correct wiring? Yes or NO?

Please, answer like this: YES or NO.

So the Voltages are:

on the OT with Power Tubes Mounted on, Amp powered on and no speaker connected:

pin 6/7 = 306V
pin 12 = 299V
pin 13 = -15,85 V

Resistance between 6/7 and 12 is 252 Ohm

Resistance between 6/7 and 13 is infinite, no connection...

The Amp is actually working, as you can see in the picture one Power is Glowing more than the other, the one more lighten is the one with lower bias voltage...

Ok, Thanks for your answer. Do I have to measure the voltages on pin 6/7 and 12 and 13 of the output transformer WITH or WITHOUT the speaker connected? I only got a 8 Ohm Speaker… And I'm using juste the 8 Ohm output, even if the 4 and 16 Ohm outputs are mounted and connected to the OT as the project...
Another question: when you tell me to measure the resistance betweem 6/7 and 12, 6/7 and 13, Can I just unplug power tubes or do I have to unplug even the preamp tubes? Speaker must be connected or not?

Thanks.

Yes, resistors are correct values,

On PIN 5 without tubes, as I've written in the first topic are symmetric, -23 V on both sockets

Hi to all,

I've assembled the kit A15MK2, I've reach the final step: mount the tubes and check the bias voltage.

On V5 pin 8 I set 33,5mv but on V6 I read only 19mV!

The tube vith lower voltage died, I've tried a matched pair of Tung-Sol 6V6GT but same problem! 34mV on V5 and 19mV on V6...

Voltages measured on pins of the tube sockets WITHOUT TUBES are perfectly matched:

V5: Pin 4 = 348V ; Pin 5 = -23V

V6: Pin 4 = 348 V ; Pin 5 = -23V

At the exit of the Power Supply Board, the blue wire that goes from the board to the lugs (lug nr. 6 of the board counting from down to up as shown in the layout, the pin in front of C28 on the left) I measure WITHOUT TUBES 347V

Please Help me found what's wrong!

Thanks!