Author Topic: Mesa JCM800 restoration  (Read 6184 times)

soldersqueeze

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Re: Mesa JCM800 restoration
« Reply #15 on: September 12, 2013, 03:55:34 AM »
Damn, this is epic! Really great work as usual, guys.

Geez, i wish You 2 were my mates that fixed my broken shit and made it better than new, awesome as always  :)

+1

peterc

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Re: Mesa JCM800 restoration
« Reply #16 on: September 12, 2013, 12:12:47 PM »
Quote
Using Rick Holt's 555 SMPS (http://www.diystompboxes.com/smfforum/index.php?topic=74088.120 Page 6-7). Though Cleggy has used a bigger inductor. Tried a Nixie PSU and it created a lot of noise for some reason. This one is not ideal on vero, but seems to work fine. It's been given a good long test.
Quote

Thanks for that.
Peter
« Last Edit: September 14, 2013, 01:56:56 PM by peterc »
Affiliation: bizzaraudio.com

marauder

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Re: Mesa JCM800 restoration
« Reply #17 on: September 12, 2013, 12:42:14 PM »
This is the original article about the PSU
http://www.ledsales.com.au/kits/nixie_supply.pdf

Reading the DIYSB thread it seems that a 150uH inductor is better than the original 100uH, mine is a 120uH, 2.5A rated one, it doesnt get hot, but the mosfet does and needs a heatsink.

The vero layout is slightly wrong, the 2.2k and 100pf are on the wrong side of the UF4004 diode.


« Last Edit: September 12, 2013, 12:43:57 PM by marauder »

gtangas

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Re: Mesa JCM800 restoration
« Reply #18 on: September 12, 2013, 02:42:19 PM »
Hey...

I have one vtwin open in my table with a stupid problem
.maybe you can help me

The previous owner send it to repair but on the OD channel the output is to weak.you can ear it but...

From the look of the PCB only the vActrols was changed y new ones. Can I jumper the ldr side of the vactrol just to check if the problem is there?

Thx
Sérgio



marauder

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Re: Mesa JCM800 restoration
« Reply #19 on: September 12, 2013, 03:02:02 PM »
Should work jumping the resistor side of the vactrols.  What vactols are they?  This one had VTL5C9s.

Here's a schematic.
http://tubefreak.com/v-twinp.gif

gtangas

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Re: Mesa JCM800 restoration
« Reply #20 on: September 13, 2013, 04:49:16 AM »
i will post some pics later

gtangas

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Re: Mesa JCM800 restoration
« Reply #21 on: September 14, 2013, 06:20:37 AM »






I think this one was in time moded...

marauder

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Re: Mesa JCM800 restoration
« Reply #22 on: September 16, 2013, 03:59:59 AM »
No idea what's going on there.

The jfet is part of the bypass switching.  Is the cap connected between the jfet and pot?


gtangas

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Re: Mesa JCM800 restoration
« Reply #23 on: September 16, 2013, 10:22:42 AM »
Yes it's connected to the pot...
The problem with this units is low gain
The tubes are new and the vactrols ware replaced by a guy

Do you think the problem could be on that cap?

Vallhagen

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Re: Mesa JCM800 restoration
« Reply #24 on: September 17, 2013, 01:04:23 PM »
Fantastic and ambitious job! Im impressed!

Yes i still have Blüe Monster pcb-s for sale!

...and checkout: https://moodysounds.se/

masterlk

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Re: Mesa JCM800 restoration
« Reply #25 on: September 17, 2013, 01:51:39 PM »