JTM45 Parts

Littlewyan · Post by **Littlewyan** » Sun May 17, 2015 9:21 am

I'll stick to Carbon Films across the board I think, with WW for the screen grids and MO for the voltage droppers.

With regards to caps I'm ordering new silver mica but have also bought a lot of 40 old ceramics. I'm going with the spec you mentioned, 500/560pf mixer bypass, 250/270pf tonestack and 100pF Bright cap. I have seen a few images of old JTM45s with 250pF bright cap as stock, but these were very early ones from 63 that also had carbon comp resistors. After that like you say its all 100pF bright cap.

Not decided what I'm going to use to start with though. Its my understanding that old ceramics make the amp slightly more aggressive sounding? Whereas the new silver micas are cleaner sounding with high end that goes on for days?

I did have a chance to buy a lot of old RS Silver micas on ebay but got outbid and really regret not bidding more!

Littlewyan · Post by **Littlewyan** » Wed May 20, 2015 1:09 pm

I'm now considering buying a transformer set from Classic Tone for this. I already have a 6.6K JTM45 OT from Danbury in the UK but I think 6.6K will be too clean for my taste. Anyway I've read that a few people get a high B+ with the classic tone PT, 470V! Is this a common issue or just an issue with users in the US? I'm in the UK and my mains tends to run at 240VAC dead on.

ivan H · Post by **ivan H** » Wed May 20, 2015 8:11 pm

Hi, if u r after the proper B+ voltage I would suggest a 1202-55 off Brian at Marstran. I have one & with our Australian wall supply of 240VAC & a JJ GZ34 B+ is, IIRC, 446V. This is with a -139 OT & EL34's. This PT is a little under spec for EL34's but I used it as I wanted the "sag" under load. Using even a used Mullard rectifier should bring the B+ up a few volts to between the 450 ~ 460 of the originals. Hope this helps. Cheers

Roe · Post by **Roe** » Thu May 21, 2015 4:38 am

Littlewyan wrote:I'm now considering buying a transformer set from Classic Tone for this. I already have a 6.6K JTM45 OT from Danbury in the UK but I think 6.6K will be too clean for my taste. Anyway I've read that a few people get a high B+ with the classic tone PT, 470V! Is this a common issue or just an issue with users in the US? I'm in the UK and my mains tends to run at 240VAC dead on.

I got 465+v with the 230v primary and 440+v with the 240v primary. This is running the high voltage secondaries

Littlewyan · Post by **Littlewyan** » Thu May 21, 2015 7:00 am

It should handle EL34s fine as I believe both the KT66 and EL34 PTs can only handle 150mA.

Sounds like the Classic Tone will be fine. How do you find the OT Roe?

ivan H · Post by **ivan H** » Fri May 22, 2015 2:10 am

Littlewyan wrote:It should handle EL34s fine as I believe both the KT66 and EL34 PTs can only handle 150mA. ?

Hi, yes it handles it without a problem, tho the 1202-133 PT is the one that was used for EL34's. Same voltages as the 1202-55 but a bit higher current, I believe. Wasn't used a great deal, the slightly lower voltage 1202-118 being much more common. Cheers

Littlewyan · Post by **Littlewyan** » Fri May 22, 2015 2:56 am

Ah sorry I see now. Marshall used more transformers over the years than I thought!

I'm trying to decide at the moment whether I want to have a transitional amp with EL34s or to stick with the KT66s. After listening to clips of KT66 amps the KT66 valves don't seem to have as smooth of a tone as the EL34s and the EL34s have that nice upper mid range. Plus I don't think a standard JTM45 will have enough gain for my liking.

Metropoulos Forum

JTM45 Parts

Re: JTM45 Parts

Re: JTM45 Parts

Re: JTM45 Parts

Re: JTM45 Parts

Re: JTM45 Parts

Re: JTM45 Parts

Re: JTM45 Parts