Tube Amp Archive

Hi Rooster, just spotted this thread and wanted to add my support. I've been road testing a LarMar MV in my Express clone for the last few months and it works great for my setup. I think it does reduce the compression slightly in the output stage, but for me that's a good thing as it means I get a s...

The original R31 was 47k and raising the value to 56k had the opposite effect of giving me less bias voltage. So I went the other way, with the 22k getting me in the zone. As for the trimmer pot I was assuming it was 25k, it's marked on Ceriatone layout as 22k, so I just had a look and found it to b...

Dave, I'm definately having fun but no plans to build another amp just yet. Would be nice to actually play some guitar inbetween this endless search for tone! It's hard to give a full appraisal of the amp using the speaker I have at home, and it's so loud that it'll have to wait 'til I'm back at the...

OK, I put the 1 ohm resistors in place and set about adjusting the bias. The 4k7 R25 is still in place by the way. The max voltage I could get across the 1 ohm was 26mv with the bias trimmer up full, while increasing this voltage the plate voltage decreased to 488. So, 488x0.026=12.7w static dissipa...

Dave O - I've got EL34M's in the output, not sure what the M denotes. I agree that ultimately it's the sound that matters. I've just stuck a few old valves in it to get it up and running and already I like what I'm hearing. As you state, my major concern was running the valves within their safe oper...

Dave,
I've just changed R25 to a 4k7 10watter. It brought B+ down by a small margin to 490v and B+2 to 452v.

I measured the voltage across R20 at 1.16v and across R21 at 0.76v.

Is this useful, I can quite easily put the 1k back into the equation and measure R20/21 again?

Hi Rob, yeah I've been in full mad scientist mode the last few days..........loving it!

Note to self: Eat and wash occasionally.

Check out http://www.hificollective.co.uk and find the 1W Holco H2 1ohm resistors. They're not cheap but they're 0.5% tolerance, so perfect for this application and it's not like you need a load of them. I've already looked at hifi collective as they have a nice range of quality resistors, but when...

Mouser is the only place that I've seen the 25w cement type resistors, the down side is the shipping costs at £12 for an 0.82p component. I thought I could make it worthwhile by fleshing out the order with a few other things that I need, but of course they didn't stock them at Mouser - they stock th...

Thanks Dave, that really is awesome! And yes it does feel good...........it was never about creating a clone as such, just using what was available. I need to get hold of a few bits before I can try these suggestions. Can the 1 ohm resistor be left in place? Or does it need to be removed and replace...

Just got back from rehearsal room and managed to have a blast with the ‘Carlspress’ and must say that I really like it! I’m fortunate enough to have a Ron Worley built clone at the room which is spec’d pretty close to an original so I could do a direct comparison. The Carlspress was slightly less fo...

Thanks ampgeek, it appears your diagnosis was spot on. Removed the feedback wire and hey, it worked. So I swapped the OT wires and replaced the feedback wire and hey, hey, it still works! Didn't have time to correctly measure everything but it's still at the 500v mark with everything connected and r...

Thanks all, I will try disconnecting the presence feedback and see if it makes a difference. Will the el34s stand up to 500v ok? I'm a little concerned about it frying the few that I've got. Does anyone have any experience of the zener diode trick? I've seen a few express inspired schematics that us...

Thanks Cliff.

A different PT would certainly help the situation but I was looking for any tips that may bring the voltage down without a need for new one.

Lead dress issues will be dealt with when I reach that hurdle.......

‘Total novice biting off more than he can chew’ alert! Hi folks, I recently acquired a Carlsbro 50 Top amp head which isn’t really suitable to my style, so I thought why not turn it into an Express. Easy peasy! Main problem being I’ve never built an amp before but I can follow instructions and use a...