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Kelvin Tyler
Reply with quote  #16 
Small correction.
Stephane. Looks like I need to go back to elementary school! For the 12AT7 tube heater power consumption is 12x0.15=1.8VA so 4 tubes would take 7.2VA. This would still give you a total power requirement of less than 130VA. Previous comments apply. Sorry for the confusion[confused].
Regards
Kelvin
Stephane Bureau
Reply with quote  #17 
Thank you for the update. My amp gives me the sweetest sound I have ever heard. I just bought 4 NOS 6P45S for about 60 US $ to hear if it makes a difference because some of my used tubes have worst specs than the others, and I don't have a tube tester, so now I trust what my seller wrote on them. My next project will be the Grounded grid preamp in the audio reality book. But I saw on the net that there are 2 PCBs. Do you know if we can take some drawings and ask a company to make them or go point to point ?
Kelvin Tyler
Reply with quote  #18 
Stephane. Yes, the SOB is a very sweet sounding amp. I hope you get as much enjoyment from your build as I have from mine.
As far as the GG preamp is concerned, if you wish to get up and going quickly then buy the kit. It is excellent value and saves you from 'metal bashing' and layout problems. I cannot recommend that you attempt to copy Bruce's PCBs.
If you wish to get your hands dirty go for a point-to-point build. In this case keep all power supply components well clear of the preamp circuit. I built mine in two separate die-cast boxes. For simplicity I only included one set of inputs. I do not think you will save much money going this route as the kit is very keenly priced. There is of course the satisfaction of doing all the construction yourself and the article in Audio Reality makes this an easy build.
Whichever route you take I am sure you will be delighted by the sonic results. Just do not use unduly long interconnects to your SOB.
Regards,
Kelvin
Carson
Reply with quote  #19 
You can easily build a scratch GG after tackling the SOB
Stephane Bureau
Reply with quote  #20 
Quote:
Originally Posted by Kelvin Tyler
Stephane. Yes, the SOB is a very sweet sounding amp. I hope you get as much enjoyment from your build as I have from mine.
As far as the GG preamp is concerned, if you wish to get up and going quickly then buy the kit. It is excellent value and saves you from 'metal bashing' and layout problems. I cannot recommend that you attempt to copy Bruce's PCBs.
If you wish to get your hands dirty go for a point-to-point build. In this case keep all power supply components well clear of the preamp circuit. I built mine in two separate die-cast boxes. For simplicity I only included one set of inputs. I do not think you will save much money going this route as the kit is very keenly priced. There is of course the satisfaction of doing all the construction yourself and the article in Audio Reality makes this an easy build.
Whichever route you take I am sure you will be delighted by the sonic results. Just do not use unduly long interconnects to your SOB.
Regards,
Kelvin


I have a problem and after many hours verifying the amp, I am still without a clue. The tube fuse of V5B and V6B blew up twice in th same day. I don't have reference voltages at the tube pins and since the amp is very big, I am afraid to test it live with tubes. I would have to put it on his side. So I checked the circuit on the good channel and compared it to the problematic one. No clue. I get distortion on channel B then half an hour after the fuse blows. Too much current is passing through these two tubes, so can it be a bad resistor going to output tubes or to the two 12AT7 on that channel ? Thanks for your great advices.


Kelvin Tyler
Reply with quote  #21 
Stephane. V5b and V6B are the lower two output tubes of the B channel. One of these tubes could be faulty or, possibly, the B- bias has been lost. Since the B- bias comes from the same point as the A- bias, ie the junction of R37 and Z6, and the A channel is working OK you should carefully check the resistors R14B, R17B and R18B which connect the bias to the grids of the B channel lower tubes.
If no fault is found with these connections, try swapping the V5b and V6B tubes with those from the A channel which we know are OK.
Kelvin
Stephane Bureau
Reply with quote  #22 
I switched the tubes and for now I don't hear distortion. I will have to build a tube tester too. Do you know how Mr Rozenblit chose his chokes for the SOB ? They are 0,035 H and for example for my guitar amp, it is a 5 H. Maybe it is a long formula that only engineers understand. Another thing, I find my SOB lacks power and I wonder if I should buy Audio Reality and build a T8 or T16. Why are they not on sale on the site ? The new concepts are better ? Thanks.

Kelvin Tyler
Reply with quote  #23 
Stephane. The choke and following large capacitor (C8 or C10) form an attenuator for AC ripple on the B+ or B- lines. Without going into too much detail, the 0.035F choke and 2200mFd cap give a reduction in ripple at 100Hz of ~30, which is adequate here.. A 5H choke capable of carrying the sort of currents in the SOB would be a much more massive affair.
With the type of tube you are using it is especially important that the pins are clean and they are well seated in their sockets,
Bruce is an innovative designer and has evolved his circuits both in respect of performance and cost. His kits afford unmatched value for money. He has named his latest amp 'Pinnacle' for good reason.
Power requirements depend on many factors including personal needs, speakers, listening environment, etc.
Audio Reallity is very well worth studying.
Regards,
Kelvin
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