EEC83 valve for JCM800

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petejt

petejt

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I was going to call this thread "My amp died last night"...but after seeing the thread about BeZo's drummer, I thought that'd be in bad taste and disrespect towards him.

Anyway, I was at a blues jam last night- I just brought my Marshall 50 watt JCM 800 slaved via a THD Hotplate into my Roland Jazz Chorus. It had been a few weeks since I last played it but thought it'd be fine. I turned it on, tried all sorts of settings, ended up cranking everything up to the moon- and bugga all sound......

One of the guys in the blues jam was an old muso who has been around for yonks...he genuinely seemed to know what he was talking about, and said the problem was that the "EEC83" valve needed replacing. I thought it might have been the poweramp valves dying, but he said they wouldn't be.

Anyway, I wasn't aware until just now that the EEC83 is also the 12AX7 preamp valve, or so what I've read.

So I thought I'd better take the amp in for a tune-up while I am at it getting the preamp valve replaced. No modding- in fact someone stuffed around with the circuit on the Hi Input with a half-arsed Jose' Mod before I bought it, so I want that removed.

What preamp valves in particular would you recommend? Should I get an SPAX7 like in my MarkIV? I want a full-bodied, rich warm sound that sounds really nice when clean, as I can just push the amp with my dirt pedal for high gain stuff. I've got the MarkIV for cranked amp gain...
 
The Matsushita is a great flashing starting tube, with a lot of highs and little bit of a hiss especially when new. I have squirreled a lot of them away and have realised that my amps get a little bit thin with using them on every position. I would not use more than one on either V2 or V3.

In my Marshall I prefer kind of Philips/Valvo/Mullard types of ECC83's. Gives you what you expect from a Marshall. To reduce brightness I tend to use Tungsram or Reytheon black plates.

"Rich and warm" - If you'd like to increase gain as well (Sylvania) 7025's are a great choice.
 
being in australia and espically perth any sort of nos tubes are going to cost a fortune i liked the sovtek lps in v1
 
Morning!! I just tuned one of these up a couple days ago and used run-of-the-mill JJ ECC83s in all 3 preamp sockets. The amp sounded great!! Furthermore, I tried a mess of different powertubes in it as well, and due to the higher PV (was running at 486V), I ended up using a matched pair of JJ EL34s biased at 32mA each. Amp roars now.

I'm only saying this because I was surprised the JJs sounded as good as they did. I'm typically not a fan of JJ glass, but in this particular amp, it killed.

A full complement of glass (all 5 tubes) should run $50 give or take, and I'd suggest going with all new glass if it's not been done for a while. The bias trim pot is totally visible and accessible underneath the chassis.

Good luck,
Mo
 
ECC83 = 12AX7

Please note that sometimes what differentiates the two is the plate length, and from what little I know about Marshall amps, they tend to like short plate lengths in the preamp socket tubes; which may be why they're into ECC83s as opposed to a host of other 12AX7s.
 
vic":qyyruncc said:
being in australia and espically perth any sort of nos tubes are going to cost a fortune i liked the sovtek lps in v1
Click to expand...

Nah I wouldn't worry about NOS valves. Thanks though.
 
Ventura":10q72kri said:
ECC83 = 12AX7

Please note that sometimes what differentiates the two is the plate length, and from what little I know about Marshall amps, they tend to like short plate lengths in the preamp socket tubes; which may be why they're into ECC83s as opposed to a host of other 12AX7s.
Click to expand...

Ah okay. Thanks Ventura. We opened it up today and yep it does have preamp valves with short plate lengths.

Apparently when we hooked it up to a a Randall 4x12 cab and plugged in a guitar, it worked perfectly! Not even noisy apart from the slight 50Hz power hum. Oh and we did take the covers off the preamp valves too :D . It was brilliant, I couldn't believe it. It sounded so glassy for cleans, and when opened up had that awesome bark and roar.

So from that we worked out that it must have been a bad speaker cable that I used to slave the amp into my Jazz Chorus combo amp. A really shitty one! But I did decide to get the poweramp valves changed out in a few weeks- I want some nice Svetlana EL34s. Maybe SED WInged Cs but I'm happy with the New Sensor version. I also decided to get four proper good quality speaker cables made up, to prevent this problem in the future.


Thanks again for all your help guys. Much appreciated.
 
:thumbsup: Glad it worked, and hey, you can call me Mo

Peace,
Mojo :yes:
 
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