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Early RD-50 version?


Lars Verholt (lmv)
Username: lmv

Registered: 11-2009
Posted on Saturday, November 28, 2009 - 05:11 pm:   

Hi there,
I recently rescued an RD-50 110. The poor thing came to me without the speaker, shot reverb tank and some bad cross-over distortion. During the repair process I discovered that the amp is a version not documented by the schematics found on this website. It has 27 ohm cathode resistors and the base bias voltage is derived by a 43k resistor from the 30V grid supply (one for each transistor). Does anybody have a schematic of this type? Would be cool to have it properly documented.
-Lars Verholt
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Sunday, November 29, 2009 - 12:51 am:   

Lars,I may be wrong but it sounds like you got one of those in between proto-type models.There was a period where musicman hired new designers and tinkered with the layout of the circuits.You seem to be a pro at working on this kind of stuff.So, If I had to work on this thing I would use the schematics from this site and replace all the different inprovements they tried to make.Then if you want to make that head better Ed Goforth has tons of great mods and ideas for it ,best of luck,Bill
Lars Verholt (lmv)
Username: lmv

Registered: 11-2009
Posted on Sunday, November 29, 2009 - 10:56 am:   

Hi Bill,
thank you for the quick response and thanks for confirming my thought that this is an 'odd-ball' version. For general info I should mention that the new speaker I put in the amp is an Eminence Copperhead. Although I am not much of a 'mod' guy, I am considering making a change in the circuit to have the bright control on the footswitch instead of the reverb (which I always leave on anyway).

All the best,
-Lars Verholt

Reviving this Thread

I have two RD 50 110s like that, dated 11/80 and 12/80. Both have the 27 ohm resistors, the 470 resistor in a different location and some other resistor value differences. The zener went bad and fried the 470 prior to my ownership, along with IC-4. All good now.

ed_goforth's picture

RD-50 MOD tank upgrade

For those experiencing drenched reverb right off the bat with the Long delay 3-spring tanks (MOD Reverb Tank, 8EB3C1B Short 3 Spring Long Decay), Be sure to change the 25k Linear reverb control pot to a 25k Log (Audio taper) pot for more control on the low end of the reverb, You can still crank the Reverb if you wan to surf! :)

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