JTM45 Question

Gassage

Which reissues are KT66 equipped?

thx

ecc83

Looking at an EL34 schematic I don't think there is much to do except a bias setting? You would need to do that for any valve change anyway. I am sure ICBM will put us right before long?

Dave.

Gassage

ecc83 said:

Looking at an EL34 schematic I don't think there is much to do except a bias setting? You would need to do that for any valve change anyway. I am sure ICBM will put us right before long?

Dave.

5881 version?

GavRichList

my understanding is that they're interchangeable, subject to the usual bias. 

Gassage

Cheers Gav

GavRichList

No worries. If you're thinking about getting one...do! Bloody lovely thing. My favourite amp, fwiw. Oh, and if you get one, don't use the standby switch - Rectifier killer. 

ecc83

"and if you get one, don't use the standby switch - Rectifier killer." I know a mod for that if anyone is interested.

Dave.

ICBM

All reissue JTM45s use 6L6-family valves, so can use KT66s with just a bias adjustment if necessary.

Reissues omit the small cap on the upstream side of the standby switch, which can be fitted to reduce the possibility of the rectifier arcing when using the standby. Originals had the cap, so it’s more historically correct anyway.

ecc83

Hi IC, the schematic I found shows a total of 64uF on the cathode of the GZ34 and that is the absolute valve data max and allowing for the wide tolerance of electros AND rubbish modern rectifiers I am not surprised they die! I would put 10 Ohms between the two caps. And JUST to further upset the cork sniffers! A 1N4007 in each anode!

Dave.

breadfan

ecc83 said:

"and if you get one, don't use the standby switch - Rectifier killer." I know a mod for that if anyone is interested.

Dave.

I’ve heard this about AC30s but never JTM45s.

I have a Gartone clone & always use the standby switch.

Is the mod common?

Gassage

Well- my question is moot now as I bought a Lerxst instead!

ecc83

breadfan said:

ecc83 said:

"and if you get one, don't use the standby switch - Rectifier killer." I know a mod for that if anyone is interested.

Dave.

I’ve heard this about AC30s but never JTM45s.

I have a Gartone clone & always use the standby switch.

Is the mod common?

I doubt it! It uses those 'Devices of Old Nick, modern thermistors and (eeek!) SILICON diodes!

Dave.