Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: guitardude57 on June 03, 2016, 06:48:22 pm

Title: Randall RD 45
Post by: guitardude57 on June 03, 2016, 06:48:22 pm

Anyone per chance have a schemo for the Randall RD 45 amp?


Thanx

Title: Re: Randall RD 45
Post by: guitardude57 on June 06, 2016, 11:21:50 am

Got the Schemo from Randall, nice.

Title: Re: Randall RD 45
Post by: Willabe on June 07, 2016, 07:25:20 pm

Yes, nice.  :icon_biggrin:

Title: Re: Randall RD 45
Post by: Theta on December 21, 2017, 04:12:18 am

Quote from: guitardude57 on June 06, 2016, 11:21:50 am

Got the Schemo from Randall, nice.

Sorry for necro this thread, but any chance you can forward that schematic for me please?
Randall don't answer my emails and they don't provide me any details regarding my RD45 amp...
I've found the schematic sonly for the RD50 which is a total different amp (cathode biased etc.)
thanks

Title: Re: Randall RD 45
Post by: guitardude57 on December 21, 2017, 10:41:33 pm

Sure... what is yours doing?

Title: Re: Randall RD 45
Post by: guitardude57 on December 21, 2017, 10:55:32 pm

Here is the Schematic for the RD 20 and RD 45...

Title: Re: Randall RD 45
Post by: guitardude57 on December 22, 2017, 05:10:23 pm

Let me know what your problem is with yours...
Once I went over the schemo, found the problem in 15 minutes...


The one I have, I got from a tech that couldn't figure it out... Had no signal go past the input.
He evidently thought the Cliff jack had buggered up.  So he replaced it, and no joy.


The amp has an opto on the input...it was bad.  And to further confound things, the right hand
break Cliff Jack, was replaced with a Left Hand break jack.  So when you plugged a cable into the input,
the jack shunted the tip to ground. :dontknow:


I happened to have a new Cliff hanging out... so I disassembled it, and reversed the parts to make a right hand break jack.  Replaced the $2 Fairchild Opto... been working ever since.  There are 5 Optos in these.  A few for the channel switching, and a couple for the boost function.  It really is a nice amp.  I kept it.

Title: Re: Randall RD 45
Post by: Theta on January 14, 2018, 03:26:49 am

Quote from: guitardude57 on December 21, 2017, 10:55:32 pm

Here is the Schematic for the RD 20 and RD 45...

Thank you so much!!!
Sorry for the late response.

My issue is really weird: Just like another guy (here: http://music-electronics-forum.com/t43818/ (http://music-electronics-forum.com/t43818/))
I got an oscillating Randall RD45.
Clean channel is ok. with or without boost.
But on the OD channel, when activating Boost, one of the stages is oscillating / hums like hell.  Anything above 11 o'clock on gain.
Swapping tubes ( V1, V2) did not help. 
OD Channel without the boost is fine and quiet.

The guy mentioned above wrote:
"I'll try to fix it with a snubber cap (100pF) across V2's plate resistor(s), but maybe there's some better cure?
Thanks for help and informations"
But that was his last comment in 2007...

Any idea?
Thank you again.

Title: Re: Randall RD 45
Post by: Theta on January 17, 2018, 05:04:36 pm

ok,  think i found where this noise was oncoming from. It was not the amp. (Luckily)
:)