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1  Muchless / DC 30 / Re: Hum caused by fried resistors? on: April 05, 2014, 11:09:39 PM
Never mind, looked a bit more closely at the schematic, dual 250K, but log or linear?
2  Muchless / DC 30 / Re: Hum caused by fried resistors? on: April 05, 2014, 01:10:06 PM
So I replaced the four fried resistors and all was well for a few weeks, then last night a different pair fried.  Replaced them, and then this afternoon one of the original replacements blew again.

I'd switched a few things around as I went (like the rectifier tubes, I was using a pair of old ) and I came to the conclusion that the real culprit was the output tubes. Replaced the latest resistor (this time it was just the 1.5K 1w, not both it and the 100 ohm 3w), replaced all the output tubes and now the hum has gone, it was all back to normal for about 10 minutes except that now the master volume pot seems to be screwed, various dead spots between off and 10 o'clock and generally scratchy sounding.

It looks on the schematics to be a dual-gang 2.2M, can anyone confirm this please?

Beginning to wish I'd just dropped the extra $$$ to get a real Matchless...
3  Muchless / DC 30 / Hum caused by fried resistors? on: March 09, 2014, 01:34:13 AM
I was playing with some friends last weekend at fairly low volumes and after about 20 minutes my Dizzy 30 made some horrible noises, then went silent, at which point I realised there was smoke coming out of the input jacks and wafting out of the back.  I had recently re-wired the speakers (a Celestion Blue and a G12H30) to be parallel instead of series by having a cable from each of them and using both of the speaker plugs, as according to the schematic these are in parallel.

And yes, I changed the impedance switch to 4 ohms.  I had been playing at home like that for a couple of weeks and everything sounded fine.

I thought that maybe I had misinterpreted the schematic and had blown the output transformer.  I wondered whether it was the whole thing or maybe just the 4 ohm output, so I unplugged one speaker, switched to 8 ohms and turned it back on.  Surprisingly it worked, which was lucky because I had a gig that night, which also went fine, even at medium volumes, although there's been a low level hum that I don't think used to be there.

Meanwhile, during the week some new EF-86 valves I ordered on eBay months ago finally turned up, so I've been swapping them around all week and having fun.

I wanted to see if I could figure out where the hum was coming from.  After eliminating the pre-amp as the source I decided to try swapping some output valves around (I have some JJ's that came with it and some Sovtek EL34Ms which I think sound better, but they all worked fine as far as I could tell.)

After trying a few combinations suddenly there's more bad noises and silence and smoke.  Fearing that the output transformer had gone for good I opened everything up, and the picture is below.  Can't see any scoring anywhere, what seems to be fried are the resistors on the output valves on one side (circled).  I also noticed that there is a brown wire that is lodged between the pins of one of the output valves (arrow on the diagram), and that it looks like the insulation may have melted.

This was built at Ceriatone, not by me, and everything else looks great, but surely that wire's not supposed to be there?  I'm in Australia, what are my options for getting it fixed?

4  Muchless / DC 30 / Re: ABY switch for DC 30, what about the "Y"? on: January 20, 2014, 09:28:54 PM
You can do it by just running a patch cable from the second input of the channel you're plugged into into the top input of the ther channel.  It does change the sound slightly, but I'm not sure whether that's due to the load on the cable changing or having both channels running at the same time.

I'm looking for a buffered ab/y that lets you adjust the relative gain of each.
5  Muchless / DC 30 / Re: O-rings on: January 20, 2014, 09:16:05 PM
Thanks but how do you use them?  Where do they go?  And do I need all three?
6  Muchless / DC 30 / O-rings on: September 29, 2013, 10:55:32 PM
I just got my Dizzy, it sounds amazing but do I need the o-rings? Where do they go?  I'm guessing on the 12AX7s but at the top or the bottom?
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