• Registered: 2009-01-01
  • Posts: 665

Topic: JCM800 2210 bias pot

Could anyone tell me where I find the bias pot in a JCM800 2210? I would have thought it's near the power tubes but can't see anything? I can't see the red and black jacks either (to insert the multimeter tips).

  • From: Florida, USA
  • Registered: 2008-06-04
  • Posts: 1,420

Re: JCM800 2210 bias pot

If the amp does not have external bias pots (like the JCM2000 series) they'll likely be inside the amp.  You'll probably have to take the amp out of it's head shell.  If you are not extremely comfortable inside amps and/or do not know how to properly discharge the capacitors I'd bring it to a qualified technician.  Be very careful, these things can shock the hell out of you!!!

'67 and '74 Fender Twin Reverbs, '74 Marshall 1987 lead mkII, Metro Superlead 100. Pedals from TC Electronic, Ibanez, Dunlop, BK Butler, Electro-Harmonix, Fulltone, Maestro/Gibson, Loopmaster switching, VoodooLab, Boss. Gibson and Fender guitars, Dimarzio pickups.
  • Registered: 2009-01-01
  • Posts: 665

Re: JCM800 2210 bias pot

I suspected I might have to pull out the chassis. That's a bit of a drag. What will I have to do if there are no jacks for the multimeter tips?
So far I've only replaced some of the preamp tubes. I have Tung-Sols now in V1 and V5. The difference is incredible! So I'm planning a complete retube.
Im suspect V1 is the first gain stage and V5 the phase inverter. Is post #1719 correct here? http://www.marshallforum.com/marshall-a … ow-58.html
Which tubes would you recommend? In particular in V2, the cathode follower slot?

  • From: Florida, USA
  • Registered: 2008-06-04
  • Posts: 1,420

Re: JCM800 2210 bias pot

On my Superlead, there is a bias pot that you can adjust.  The Black wire is grounded to the chassis and the red is placed on Pin 1 of V1 if I remember correctly (the blue wire).  Again, these things can kill you so be very careful.  I'd bring it to a quailified technician especially being that it is a PCB type amp.

'67 and '74 Fender Twin Reverbs, '74 Marshall 1987 lead mkII, Metro Superlead 100. Pedals from TC Electronic, Ibanez, Dunlop, BK Butler, Electro-Harmonix, Fulltone, Maestro/Gibson, Loopmaster switching, VoodooLab, Boss. Gibson and Fender guitars, Dimarzio pickups.
  • Registered: 2009-01-01
  • Posts: 665

Re: JCM800 2210 bias pot

Thanks stratpaul (or Justin, right?). I'll take it to a tech I know pretty well and have him show me how to do it in future. I can bias all my other amps without a problem but they all have external pots and red/black jacks.
The amp has had all JJ tubes (power tubes and preamp). So far I've changed V1 and V2 to Tung-Sol and I can already hear an amazing difference. What power tubes (EL34) would you recommend? To bring it closest to Joe's Silver Jub tone, of course.
Which would you recommend for V2 (cathode follower?) and V3? I suppose V4 is Reverb but I don't care too much for that. I use my Holy Grail pedal via FX loop.
As a side note: I'm not impressed at all with JJ tubes. There's a distinct improvement in tone and feel of any amp that I have (mainly Marshall and various Ceriatone amps) when I swap from JJ to other brands.

  • From: Florida, USA
  • Registered: 2008-06-04
  • Posts: 1,420

Re: JCM800 2210 bias pot

I like the Wing =C=  tubes for just production tubes with great tone.  If you have the $$$ check out some NOS Siemens.  There is a guy on ebay that sells them for about $200 - $220 for a matched quad.  I use to like JJ's before they started blowing up all the time.  I have since grown to hate them and place them squarely in the "junk" catagory.  I'm pretty understanding with most products but I've had them literally KILL my amps before!

'67 and '74 Fender Twin Reverbs, '74 Marshall 1987 lead mkII, Metro Superlead 100. Pedals from TC Electronic, Ibanez, Dunlop, BK Butler, Electro-Harmonix, Fulltone, Maestro/Gibson, Loopmaster switching, VoodooLab, Boss. Gibson and Fender guitars, Dimarzio pickups.
  • Registered: 2008-10-02
  • Posts: 373

Re: JCM800 2210 bias pot

I second the Wing C I have them in the Jub and the sound great, though I think she needs a retube soon. Its been awhile since I changed them.

  • RickB
  • RickB
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  • From: San Diego
  • Registered: 2009-10-30
  • Posts: 12,198

Re: JCM800 2210 bias pot

Bluesbreaker wrote:

Thanks stratpaul (or Justin, right?). I'll take it to a tech I know pretty well and have him show me how to do it in future. I can bias all my other amps without a problem but they all have external pots and red/black jacks.

For a small charge, your tech could put in test points that are accessible for your future use to make it easy.

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  • Registered: 2009-01-01
  • Posts: 665

Re: JCM800 2210 bias pot

RickB wrote:

For a small charge, your tech could put in test points that are accessible for your future use to make it easy.

I thought about that too. Do you (or anybody else) know how to do that? Installing test points. And possibly an external bias pot.