Tube Amp Archive

True enough Martin, but it’s a gold mine if you persevere, lol.

After researching all the idiosyncrasies of the Marshall 18w normal channel and trying to solve the weird “dip” at 3/4 in the tone control as well as re-voice it into something that sounds good - I scrapped it. My “Marwatt” is now a “Dewatt”. I rebuilt the channel with a 5E3 tone stack and it is sou...

Haven’t really been enjoying my 2nd Gen lately, and it’s been rainy all day - so I made these changes after searching the forum today: https://ampgarage.com/forum/viewtopic.php?f=4&t=33286&sid=b0008ba07b0020c2937dc0b6c33dbe01 I have to say it not only made the amp sound different, it made the amp fe...

Lol, confirmation bias is a thing I guess… (pointing the finger at myself) Anyhoo, still trying to figure out what the “right” way to hook it up is then. Leaning toward disconnecting it now. - One school of thought is since it’s a parallel winding - connect it to the like-colored wires to maximize u...

So given the numbers, this winding really shouldn’t really make an audible difference then? My test yesterday wasn’t scientific by any means and my ears certainly change from day to day - and I’d rather err on the conservative side. So given factors like bass response and thermal management, - I’ll ...

Alright, got the bias sorted out and everything is running stable and quiet, so I gave it a whirl on my 2xG12H30 cab and it sounded pretty good. Nice, quiet, and stable even with both volumes dimed. I did opt to install the Lar-Mar MV, which works well and is easy enough to reverse if I grow to disl...

Ok, got everything back together and fired her up. Everything behaving as it should, let it warm up and settle down. Plate voltage settled right at 360vDC at 120vAC. The tubes are within a mV of each other and I biased it right at 41. Ran it, played it for about 40 minutes (carefully through a 1x12 ...

Never doubted you for a second Martin! I was more curious why they were paralleled than anything. Just trying to make sure it wasn’t a “happy accident” that contributed to this amps’ tone. Got all my grounding improvements and “pot dressing” done today. Yesterday I spent some time trying different d...

Here’s a pic of the marking and label shadow: IMG_0308.jpeg Actually, late last night I was searching the Marshall Amps forum and found some pretty solid clues. Turns out these are uncommon, but not unheard of. One theory has them as 70s/80s Unicord warranty transformers and another theory has them ...

Makes sense Martin. If all else is equal - let the sound determine which way to go. Spent some time today looking at any 50w Marshall schematic I could find on the internet and none are showing an OT configured this way. Really puzzling. There’s got to be an answer to “what do I have here?” somewhere…

The 20-ohm secondary you have is still a mystery. too. Any chance you miss-measured something there? That’s always possible, lol. I will say that I measured everything twice - starting fresh on two separate days - repeating each measurement twice and writing everything down as I went. The cross-mea...

Thanks for the background Roe - I figured you would know more about this OT. I appreciate you sharing your extensive knowledge and experience with Marshall amps. I’m always referencing old posts of yours to learn these details, history and fixes. So from a practical standpoint - they likely keep the...

Saw that. I think that proves there’s no real practical reason for that tap - so the juice isn’t worth the squeeze for the re-creators. I actually use that website a lot to figure out Marshall color codes. Looks like real high quality stuff; but I think I read somewhere they went out of business rec...

Here is a JTM45 version: https://ampgarage.com/forum/viewtopic.php?p=296260#p296260 You have access to the orange and green grid leads from the top of the board so you could break those and run the outputs from the dual pot back to the board. This would leave the existing grid leads running under t...

Gotcha and done. Making good progress now that my AES box has showed up. Also pretty convinced that this OT is a 783-128 repro - likely out of a Bluesbreaker reissue. All the specs I can find seem to match everything we’ve discovered through the testing. Sounded pretty good to me - far as I could te...