Problem with AR Ref 300 Mk II - any experience?


One of my Audio Research Ref 300 Mk II Power Amps has no output. Power ist ok, Switch on process is as usual, but the 8 power valves show practically no voltage when checked. The meter moves only some 3mm from the "parking position" on the left side.
Does anyone have any similar experience?
Are there any switches, additional fuses or the like, which I am not aware of?
Best regards!
Otto
ozatschek
Corrected the subject (ARC for Audio Research, not AR)
If you are on the West Coast, Gary (Hifigeek1) is an authorized ARC service tech and can he you. You can e mail him through the A'gon system. If not, call ARC and ask for Kal. He can put you in contact with a local ARC authorized service center, be it in the CONUS or elsewhere.

I'm not electronics savvy, so take with this with a half a grain of salt. But if all the power tubes are subject to the same problem, it sounds like a common power supply issue.

Good luck
Ozatschek, 2 quick follow-up points. One -- each amp weighs 132 pounds. I would try and find someone who does house calls. No joke. There's an ARC authorized service tech who lives near my house and makes house calls. He was over about 2 or 3 weeks ago to fix an open bias resister. The fix took all of 30 minutes.

Two - here's something else you can take with a grain of salt since I'm not a tech. I read the ARCDB web site description of the Ref 300. I see that it has a bunch of regulator tubes in the power supply. Wild arsed guess here .. but did you check all of the tubes, particularly the PS regulators for life? Just asking. If a blown PS tube controls the output power tubes, it might affect all of the output tubes, which is your situation.

Incidentally, regardless of how you make out, I would still contact ARC to see if the tech folks have any preventative maintenance suggestions such as replacing tubes, caps, etc. Your amp is not ready to be retired, but it ain't no spring chicken either.

Good luck and let us know how you make out.

BIF
Hi Otto,

A few weeks ago, i did have the same problem with the ARC ref 300 MK2. In my case a fuse 275mA was broken.
The fuse is located inside the amplifier on the left-backside, its easy to find because as far as i can see there is only one fuse on the printboard.
The fuse is placed between capacitor and tube V14.

I hope this information will solve your problem, succes with it!

Regards, Gert
Hi BIF: thank you for your suggestions - quite correct
(see below)

Hi Beersum8,
hi Gert,

thanks for the reply - you have been absolutly correct: the fuse war broken! I took the one from the other amp and it was up and running again.
I recognised that the broken fuse had a very thin wire within the glass cylinder, while the working one had a much thicker, spiral-like wire inside. Obviously a less sensitive type.

My original intention (when I ended up with the no-signal on all valves) was to replace the V5, that seemed to have a particular problem (it was not possible to adjust it sufficently to get the meter into the green range - although it was close to it, thats why there was no sonic
effect until now).

So I replaced it again, with the result that one component
(close to V5) got burnt, and two parts (on the V14-15-16 circuit board) kind of exploded.

I wonder if a bad tube can cause this (assuming that the replacement tube I purchased at ebay is bad - despite its detailled description). My other suspicion is, that the amp
had an old problem (I recognised some fixed circuit paths on the V5-V8 circuit board) are responsible for this.

I also wonder which type of fuse is the correct one?
If the replacement valve is really the cause for all this,
then the "thin" fuse prevented the amp the first time
(by getting broken) - but the "thick" fuse did not so
(it is still ok, althought parts of the amp got burnt).

I hope the service center of my local dealer can fix the Amp and answer my questions as well...

Best regards
Otto
Otto, you mused, "I wonder if a bad tube can cause this (assuming that the replacement tube I purchased at ebay is bad - despite its detailled description)." The answer is yes. If a tube arc'ed it can take out passives such as bias resisters. An old cap can also flames out too.

You also querried whether "the amp had an old problem (I recognised some fixed circuit paths on the V5-V8 circuit board) [which is] responsible for this." Could be. That's why I renew my suggestion that you have a training tech look the amp over. In fact both amps.

Even better, I would line up an ARC authorized tech to look the amps over. If you need help locating an ARC authorized tech, call Kal at ARC. He can help
Typo -- was in a rush. The penultimate sentence in the second paragraph should read "That's why I renew my suggestion that you have a [skilled] tech look the amp over."
Hi Bifwynne,

thank you for your input! I already decided to have our local ARC service guy look at the whole amp...
[in fact: a few days after having bought the amps, the other one has had a problem, and I had it checked completely then].

One question regarding my original V5 tube: when checking it with the right meter on the front panel, it did not reach the green area any more. I tried to adjust it, but even in the "full" position, the meter was not in the green area (but close to).
There was no acustic impact to be heard though.
Is this a sign of age of the tube?
Is it necessary to replace then - or should I wait for any acustic impact before replacing it?

Again, thank you very much,
best regards,
Otto
Output tube can go at any time. Tubes last approx. 2000 hours in ARC equipment. After that it's like Russian Roulette.
Hi Otto,

The nominal value of the fuse is 250mA/250V (fast type), so i think the fuse with the tin wire seems to be the right, original one. If you take a good look at the metal parts of the fuse you can see the value.
The fuse feeds the 8 output tubes, so if there is something wrong in that cirquit or modificated it is possible that the original fuse of 250 mA will blow-up.

Best Regard, Gert.
Otto, you wrote:

(1) "I already decided to have our local ARC service guy look at the whole amp..."

Me: Good call.

(2) "One question regarding my original V5 tube: when checking it with the right meter on the front panel, it did not reach the green area any more. I tried to adjust it, but even in the "full" position, the meter was not in the green area (but close to). There was no acustic [sic] impact to be heard though. Is this a sign of age of the tube?"

Me: It could be.

(3) "Is it necessary to replace then - or should I wait for any acustic impact before replacing it?"

Me: Absolutely not!! If those tubes are outside the 2000 use marker, as Gary (Hifigeek) said, you are living on borrowed time. The tube's propensity to fail and take out passives (e.g., bias resisters) increases with age.

Otto ... it appears that you are not sure how much time has been racked up on the tubes. I am hesitant to recommend this, but if you have serious doubts about hours of use, replace the tubes as soon as possible.

One more suggestion -- the amp is not that terribly old by ARC standards. Having said that, I find it odd that the amp may have blown other passives like caps, or required some circuit board repairs. I suggest you contact Kalvin Dahl or Chris Ossana (the Service Manager) at ARC and ask them if the local ARC tech should specifically perform certain diagnostics to ascertain whether other parts need to be replaced.

I am also hesitant to suggest my next point, but I would certainly include it in the conversation. If one of the circuit boards looks discolored because of a passive failure, I would ask Kal or Chris whether it would make more sense to simply replace the suspect board.

The Ref 300 is an expensive piece of gear. To sound its best, it should be put into tip-top operating order. That includes fresh tubes if warranted. And as I said above, I would make sure that both amps are thoroughly looked over.

P.S. Did you recently but the Ref 300? If so, I wonder if its worth returning it if that's an option.
The first problem I always see is a customer buys a used ARC amp for a good price and then after a few months the fuses start blowing or outputs start arcing. Moral...No one sells a used ARC amp at a good price with new ARC tubes in it.
The second problem I see is a customer has an ARC amp and is unaware of the elapsed time on the output tubes. One output tube arc and takes a resistor and/or a fuse with it. Customer replaces the tube and weeks later another output tube arcs and causes more damage. Moral....When output tubes start to arc, replace ALL the output tubes. This way, you don't have to worry when the next tube will fail and it's easier to keep track of elapsed tube hours when you replace them all at the same time. I also recommend to my customers that we use ARC tubes. The reason...you don't use cheap gas in a Ferrari.
Thanks to everybody for the valuable input!
I took the amp to out local ARC service center today, and asked them already for the things you suggest (cueck the circuit board, check all tubes,...).

[Because someone asked: I bought the amps 3 years ago, from
a dealer, with warrenty, at a fair but not cheap price.
So I guess this was ok, given that these amps were no
longer available. But I agree that there is always some
incertainty regarding the real hours on the tubes...]

Again: thanks to all of you, your input was valuable, I learnt a lot, and it gave me confidence that I do the right thing (having the amp checked in detail).

Regards,
Otto