• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

D150 monster amp and funny tooobz

as a common response to multiple PMs:

Would it make sense to change more/or all tube bases?
I share the opinion that it would, given the nature of the current buzz cycle while warming up. I learnt that on the V4 base example in the input stage. For that matter after I saw how easily they could get crushed, if I had a replacement socket which was a perfect fit I would have already changed 3 loosest sockets on the back plate.

As for the OS tube sockets: I would probably try first the one spare tube in different positions (they all have virtually the same value noted on the stickers which probably come from the original AR measurements). One tube kind of has glass angled a little to its metal base and some rust visible inside the base so I was always a little suspicious of it (may mean nothing since it biases Ok but..).

Please do not ask me to replace any more sockets for you. I will do that only if I keep the amp. So far I always just angled the pcbs and pulled them out only as much as the attached wiring allowed for; that way some sockets could be reached but I doubt one could replace each and every one that way. Some end up farther at the bottom and with too many wires in the way.
 
as another common reply to multiple PMs:

Guys I understand that the above price is a sticker shock for many. But it is the nature of this amp. ARC REF150 is something like $13k, right? and they started later using jfets in the input stage and lost 40lbs in weight savings in transformers and chassis. I already quoted a price of a new pair of 300Bs which is subject of another thread here.

I am not an expert on tubes but I start with what I deal with in my DIY audio practice: let us say that Pass and Audio Research are of comparable value each in their own field. A typical First Watt amp is $4k and it has 4 fets inside (either say a push-pull pair or one current source for another fet on each channel). And should I start listing what you are getting here?

Only because I want you to feel good about this I will reduce the price to US$5.6k. If I end up shipping it I will knock off another $100 to help your bottom line; for others I can include my driving it up to say Toronto kind of distance (400km from my location in Windsor/(across from Detroit)).

p.s. almost forgot to include a side thought (disclaimer): the current balanced input is DC coupled (C3 PP cap was removed). So make sure there is no DC offset coming out of your source or add the caps back in.
 
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Well for those interested I have to add this: I just listened to the amp for about three hours. Today after a thorough warm up there was very little noise left (though the buzz in the left channel came back briefly at one point). If it cleaned up that last bit right now I would have su!ch a hard time parting with it. On good material it sounds freaking aaaaawesome :bigeyes:.

I wish I had that mancave to get around its industrial look and size. Believe me, after you get it into perfect shape it will put such a smile on your face you will no longer remember any $s you spent; (I assume you have good speakers). I also kind of feel my SS amp projects are now losing the previous appeal :(, so in the near term I may be more likely to focus on the speakers.
 
I am thinking of slowly (parallel to other projects) looking into this buzz left through the warm up cycle. Before I can come up with some intelligent measurements to see if that frequency is on PS rails or elsewhere:

I was thinking of just removing a pair of OS tubes on each channel (since this is where the most heat is getting generated and I know that the issue is probably a contact since after warming up for 5min I can sometimes just give it a knock on top of the amp and the buzz in the speaker stops).

Can I just remove either pair without rebiasing to have 75W/chan and see if any of these sockets are a suspect?

What do you suggest for putting high voltages on the Oscope (some voltage divider and a cap to remove DC?), to check some points? Thx.
 
I would bite the bullet and replace all the tube sockets (small and large), but only with very high quality ones.
Intermittent contacts are too much trouble, and if even one tube socket is bad, the others are not far behind.

This is a known problem in all of the ARC amplifiers of that era. But take care with the delicate pcbs.
Doing this will replace the associated solder joints as well, which is a good thing. I would not attempt
any further troubleshooting until the sockets are replaced.
 
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