Beiträge von kordusit

Since I'm not an experienced pcb builder I think I'll just rebuild it with on the stripboard.
Thanks

Well, i prefer pcbs over stripboards, expecially for 2 channel and
hi gain amps. It's easier to build and to debug.
I'm going to rebuild my a15 because, although it works, it' a little messy (it was my first amp) and i was wondering weather I could build it on a pcb.

Hi, I would like to build a "pcb version" of the A15Mk2, has anyone already developed a pcb for it?

Thank you

This seems to involve radical changes to the a15 layout, I'm not really an expert... Do you think that the mod suggested by polifemo will works?
On the A15 manual it's said that changing the voltage divider R8/r9 will reduce or enanche power amp distortion, will this have the same effect?

Zitat von Kramusha;233509

For more headroom you can try a constant current sink. This will increase the output voltage a lot.

I will upload a picture..

Stefan

Hi, where can I find the schematics of a constant current sink?

Zitat von Kramusha;241055

:eek: What? Check your bias-circuit, there should be no AC voltage..

I think I have found the problem: i had soldered d1 with wrong polarity. Now I can regulate the bias properly. Anyway, there is still AC voltage! The current to the bias pot comes from two point of the power board, right? I have measured the voltage there and I have found no AC voltage but if I measure the voltage at the output of the pot, I found about 50V AC!

Zitat von Kramusha;241050

Pull the power tubes and measure the negative grid voltage. There should be a voltage of app. 30V.

Stefan

The negative grid is pin 5? There is a voltage of 25 V AC and 14 V DC (with a 8 ohm speaker connected)

Zitat von Kramusha;241045

Anode1: 12
Anode2: 13

4/15 is the 8 Ohm pin and 3/16 are the 8 and 4 Ohm pins!

Stefan

Thanks
There is no resistance between pin 12 and 13. It seems also that i've solved the problem. I've made the solder at v3 again and now the amp sounds! But I've another problem, I was trying to regulate the bias but I couldn't get a voltage of 35mV, I can get only 87.7 mV.

I'm not sure. Are the two anode pins pin 4/15 and 3/16? I don't measure any resistance between them.

I have finished building my A15MK2 and I have checked it with the schematics but it doesn't produce any sound at all. Once I switched it on without a cabinet by mistake. The fuse blown and I've replaced it but maybe also the OT has been damaged? Also the voltage are not exacts. The heating is only 5 V and the output of the rectifier is 230 V both measured with a cabinet connected.

Zitat von Chryz;240003

Hey,
did you adjust your Multimeter to AC?

Thanks! That was the problem ;D I was measuring DC instead than AC.

Yes, I think I have the same pt as you. But I have a problem, I have soldered the primary side but when checking the voltage my multimeter detect 0 V when the sensibility is set to 600V, and it goes crazy (displaying numbers that change quickly and never stop) when the sensibility is set lower. I'm quite a newbie so I'm not sure whether I'm checking the voltage correctly (I' touching with a lead lug 3 and with the other lug 7). All the soldering should be right: it's quite simple for the moment and I've checked everything many times.

Hi, I have a problem with the power transformer of my A15MK2. Following the plan, I should solder the power switch to lug 6 of the PT. But the lug n°6 doesn't exist! On my transformer I have, on a side, lugs 7 and 3, on the other lugs 10,12,13,15,16,18. The other numbers have no lugs.