110-RD-50 Current mods 10-17-2014
From Rev E Schematic
C35 = 4uF, C33/C34 = 100Uf, C10/C48 = 10Uf,
R61 = 15K, R9/R10 = 100K, R11 = 200K, R12/R69 = 1.82K,
150K added in series with 12AX7 pin 7, 220K from 12ax7 pin2 to ground.
47pf across R21, IC1 = OPA2604
Measurements:
C34 283V, C33 565V, C35 263V (ripple 200mvp-p), C6 194V, 67V across R9, 12AX7 pate 131V
Past repairs: Q5/Q6 (2N6488), D9 , R62, R51, R54, new pair 6L6GC (JJ brand), new 12AX7, new reverb cables.
I used to use a 833 as IC3 and IC4 but IC3 is on the +/-8V and will drop to +/-7 or less due to a resistor network that derives the voltages, so I'm leaving those as original TLO72 for now. OK to use a 833 as IC1 or IC4 since it is on the +/-16V.
Fri, 10/17/2014 - 06:08
#1
Rick Viola
My current 110 RD50
Very nice. What is the purpose of the modifications?
Mods
These are mods I collected with much research and updating to the latest distortion channel tweaks from all the forums.
C10 and 48 probably should be lowered from 10uF to 2.2uF as in the rev E schematic for less bass gain in the distortion channel but they were already installed in my amp and it is a messy change. Probably not much difference.
I edited the above and also added the 220K from 12AX7 pin2 to ground I forgot about doing (or was in my amp already).
I looked closely with a scope the last few days and discovered a few things besides leaving IC3 as a TLO72 so the +/-8V doesn't drop.
If I tweak the -8V by lowering R67 by paralleling a 5K across it, it clips centered as it should at the preamp out (IC3-1). Although, this doesn't matter since the 6L6 tubes are clipping before that, but I notice a difference in overtones audibly with a signal generator listening to the output tubes. (I'm using a high power resistor load and looking with a scope). Also lowering the negative feedback resistor R43 150K to 100k (or a 300K across the 150K) lets you turn up the volume another notch before clipping at the 6L6's (seen at my load). I'll try these two mods and see how it goes when all back together.
Update: Sounds fine. Although I don't know why an 833 op amp would load down the +/-8V more than a TL072 since the spec sheet reads the same for power supply current.
It seems I posted these changes back in 2011.
RD50 2nd Channel Mods
Like you, been collecting the mods to the Distortion channel to make it usable, but have left my early black 110 and later blonde 112 stock. The blonde 112 Distortion is much better than the 110, but not quite there yet. Would you have any sounds sample to see how it all came out? Thanks.