[John Buchanan]

Quote:

Have you replaced the capacitors in the SRM-Monitor yet, John?  It would be well worth doing and you can even upgrade the size a bit to boost performance. 

No, Birgir - I guess I'm very wary of letting anybody touch it and I figure if it ain't broke, I'm not gonna get it fixed.
The Quad ESL989 repair fiasco nearly drove me mad. 

 

[spritzer]

Quote:

 
Apparently it was to take the pro bias voltage off the trafo (and thus to compensate for that). I could ask for more details / take more pics if you want.

 
That makes no sense as the voltages in these amps are nowhere near what the Pro bias requires.  What you need is a voltage doubler off the B+ which is then trimmed to +580VDC with a voltage divider. 
 
Quote:

No, Birgir - I guess I'm very wary of letting anybody touch it and I figure if it ain't broke, I'm not gonna get it fixed.
The Quad ESL989 repair fiasco nearly drove me mad. 

 
If I'm ever down under then I'll gladly to the swap. 

 

[carbonfet]

To be fair I did ask him about an amp he hasn't had for about two years now. Who the original owner is isn't much of a secret when you can look through my feedback to find out, but you can try asking padam about it.

 

[carbonfet]

Well I finished recapping my own srm1/mk2, also took a pic of the bottom in case you can see what's going on, spritzer.
 

 

 

[spritzer]

Still doesn't make any sense.  You need a voltage doubler (two caps and two diodes) to double the B+ voltage and then trim it down again with a voltage divider.  Just get some 100nf/1000V caps, 1N4007 diodes and the correct resistors and refill the correct slots. 

 

[John Buchanan]

Quote:

If I'm ever down under then I'll gladly to the swap. 

Birgir,
you would be welcome to come and just say hello. Plenty of stuff to see and do in Perth. 
John

 

[carbonfet]

Quote:

Still doesn't make any sense.  You need a voltage doubler (two caps and two diodes) to double the B+ voltage and then trim it down again with a voltage divider.  Just get some 100nf/1000V caps, 1N4007 diodes and the correct resistors and refill the correct slots. 

 
Do you have the values of the four resistors (R301-R304) off hand? I'll probably do this after I finish building the amp which will replace it, just in case.

 

[spritzer]

R301: 51K
R302: 390K
R303: 2.2M
R304: 2.2M
 
The latter two can be substituted for one 4.7M resistor that can handle 600V+.  All the resistors are 1/2W metal film. 

 

[numbercube]

I got a used SRM-1 Mk2. 
I did the balance and offset for both channels. Thanks for the pictures, spaceace1014.
But it hums. As soon as I press the power button, the transformator (not sure) makes a hum noise.
Through earspeakers, the noise is audible when the volume pot is set to one o'clock and higher. I connected an mp3-player via cinch.
Would swapping the capacitors help? 

 

[spritzer]

So you get hum from the transformer and also through the earspeakers?  The first thing might be due to the transformer simply failing or that something is drawing too much current and overloading the trafo.  Could also be an incorrectly wired primary that is at fault. 
 
Hum on the output is possibly capacitors going bad or even rectifier diodes.  I'd change all of them for piece of mind. 

 

[numbercube]

Ok. I'm not sure yet if I send it back. Paid 220€.
 
Could you please tell me the exact part labels for the rectifier diodes?

 

[spritzer]

They used some Toshiba model but 1N4007 works just fine as a replacement.  UF4007 if you are feeling the need to spend more...

 

[crin]

i noticed that it makes quite a difference nulling balance and offset with the lid open and then closing the lid. some 9 volts to be more specific… i had to re-do all the adjustments with the lid closed—temp stability is definitely an issue! (btw the ac balance is astonishingly nice for such an old unit [mine is a mk2 with a serial number in the B 200 hundreds]—i measured ±100mV inbalance at 50 V 1kHz out.)

 

[Jonathan66100]

I noticed that too.
So I was settling the balance and offset quickly after opening the cover.

 

[crin]

i think it pays dividends to buy a trimmer screwdriver long and thin enough to adjust balance and offset through the holes in the cover and after the unit has been runinng for an hour or so.