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Not an amp but still full of lethal electricity- my effing dishwasher conked out. Thought I’d have a crack at fixing it, since I have so much time to spare. :crazy: Looks like the wash motor burnt out, since it fills and drains fine but won’t spin the washy sprayer thingies. $155 for a new pump and ...

Great work!

I've seen an arced bassman that burnt through ceramic sockets! The voltages in Jansens (and Holdens) are just unreal.

You could try larger grid resistors on the EL84s too. Never heard of the cathode zener trick - interesting idea. The grid resistors on the EL84s are currently 4.7K. What value would you suggest I try? P.S. I presume you are referring to the control grid (not the screen grid)? Yep, control grid resi...

You could try larger grid resistors on the EL84s too. Never heard of the cathode zener trick - interesting idea.

The schematic also shows the EL84 screens at 300V and the anodes at 295V - that's a bad idea for valve life and I'd recommend some screen resistors to be safe. This explains a lot :cry: Ha! Ok, more details: when the screens are at a higher voltage than the anode, they 'steal' extra current away fr...

I played thru the amp this morning (cranked) and there isn't an audible sag issue. If it sounds good then keep it, but 1k (1.23k with the internal resistance of the EZ81) is a lot of series resistance for the current drawn by the EL84s. Even if it's not sagging excessively, it could be responsible ...

How much do you need to drop the B+ by? If you're feeding the OT CT thru the 1K resistor you'll end up with a lot of sag and things will get spongy. Depending on how much voltage you need to drop, resistors between the PT and the rectifier anodes might be a better option, or a resistor between the P...

Nice build! How's the clean sound on it? Doug and Pat mention in one of their shows that the SRT doesn't really 'do' clean tones, which always puzzled me.

By ‘extract’ do you mean remove the actual drive channel components, or just reproduce it in pedal form? It’s just a TL072 stage driving both halves of a 12AX7 in succession, followed by a tone stack, so it should be easy to clone as a pedal at least.

Make sure all the pot and jack nuts and any other potential grounding points are tight. You can also plug into the return jack and see if the hum disappears - if not it's the power amp causing problems. There's not much to the power amp in these things - a couple mosfets, an opamp and then the filte...

PS: with the meter reading about 1.5 ohms measured across the speaker plug compared to across the speaker terminals...is that food for thought in amp design/electrical engineering or a well accepted loading issue when pairing trannies to valves and speakers? The resistance of speaker cable is gener...

The general rule of thumb that a single-step mismatch is usually ok seems to hold up. So 2 ohm into 4, 4 and 8, 8 and 16 shouldn’t hurt anything in the short-term, whereas a 2ohm load for a 8ohm OT (or vice versa) is ‘bad’. IMHO, the best reasons for NOT mismatching are that the tonal differences ar...

There’s loads of reasoning for both perspectives but it seems the ‘speaker-load >= OT setting’ camp predominates because it intuitively makes sense to most of us. However, there are also strong electrical engineering reasons why a speaker load lower than the transformer setting can be safer. It main...

Also, if you measured resistance on the speaker cable-end/plug, rather than the terminals on the speakers itself, it could give a slightly higher reading.

9.5 ohms resistance is not an issue for an 8 ohm impedance speaker. But I don’t think you should run a mismatch, if that’s what you’re suggesting. Might not damage anything but it won’t sound as good as proper matching.