Problem with AR Ref 300 Mk II - any experience?

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