DSL20CR - ECC832/ECC823 usage

dbf909

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I recently picked up a used DSL20CR and have been considering rolling some tubes through it. I've got quite a few old and new preamp and power tubes to play with. I've been doing a bit of investigation into what other folks have found works for them and not surprisingly there is a lot of info out there.

At the moment, the amp is sporting all original Marshall branded tubes. I've been putting it through it's paces for the last couple of days and I'm generally pleased with the way it sounds. I rolled some Speakers through it and settled on a UK G12M Greenback for now.

I've had a number of other DSLs including a JCM2K DSL50 and a DSL40C. On those amps I pretty much lived on the Green channel. I rarely used the Red channel due to the type of music I mostly play. However, the 20 doesn't have quite the range of Clean to Crunch that the other DSLs do and there seems to be a pretty dramatic step in gain from Green to Red. So I'd like to tame the Red channel a bit and see if I can reduce the gain/distortion step from one to the other.

I did pick up on a thread in my searches that discussed the use of the ECC832/ECC823 type of tube with different triodes to accomplish this to some degree. I have used 12dw7 (ECC832) in some tweed circuits to great result and I remembered that I have one or two in the tube bin (not JJs but GE or Sylvania).

In looking at the schematic for the DSL20CR (marked DSL15 but I think it is the same preamp), it looks like the Green channel only uses V1.1 (pins 1, 2, 3) and V2.2 (pins 6, 7, 8) for a total of 2 stages. Switching to the Red channel essentially adds the other two triodes - V1.2 (pins 6, 7, 8) and V2.1 (pins 1, 2, 3) - in between for a total of 4 gain stages. I could probably be satisfied with only adding a single stage for the Red channel but there is no easy way to do that without modifying the PCB to eliminate one of the stages.

Having jogged my memory of the 12DW7/ECC832 I thought maybe this would be a good approach for this amp to kind of get toward that direction - reducing the gain of one of the stages might be what I'm looking for.

So the conventional approach to doing this would be to replace V1 with one of these tubes. Half of V1 is used for both Green and Red and the other half is added just for Red, If the Red half was the lower gain triode, this would work. Unfortunately, on the 12DW7/ECC832 the high gain (100) triode is pins 6, 7, 8 and the low gain (20) triode is pins 1, 2, 3 so this would not have the result I'm looking for - the first gain stage (which is shared by both Green and Red) would get the lower gain triode and thus it would just lower the overall gain in both channels.

The obvious answer then is to use the JJ ECC823 which swaps the high and low gain triodes from the 12DW7/ECC832. With this tube in V1, the high gain (100) triode is pins 1, 2, 3 which is the shared stage. The low gain (20) triode is pins 6, 7, 8 which corresponds to the first of the 2 stages that are switched in with the Red channel. The result is that the Red channel with all 4 stages in place is not quite as gainy but the Green channel remains the same.

However, I don't have an ECC823 in my collection and they seem to be pretty rare these days so not a short term option.

But in looking at the schematic again, it appears that if I substitute a 12DW7/ECC832 for V2, it would essentially accomplish the goal. Specifically, the high gain (100) triode (pins 6, 7, 8) would be V2.2 which is shared by both Green and Red and the low gain (20) triode (pins 1, 2, 3) would be V2.1 which is the second of the 2 stages that are switched in with the Red channel. On paper and at a high level, it seems like this should work.

Now I know that in a cascaded gain design, the placement/order of the interstage gains can make as large or larger difference in the tone and drive of the circuit as the amounts of gain in each stage. So there may be some interesting effects of shuffling these around but I think that this is worth trying out.

Also, by extension, it might even make sense to sub both V1 with an ECC823 AND V2 with a 12DW7/ECC832. Then both of the stages switched into the Red channel would be lower gain but together might be just the right amount...

So if you've made it this far into the post, congratulations and thank you for bearing with me. I have a few questions - has anyone done this experiment on a DSL20CR? Is there a significant difference between the two approaches (V1 vs V2)? Has anyone tried both?

If I can find an ECC823, I will definitely try all of these combinations and report my results. In the mean time, I will try the 12DW7 in V2 in the next few days if I can find the ones I have.
 
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fitz

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Interesting. :hmm:
I have an 823 in V1 of my DSL20HR.
Never heard about the 832 in V2 thing, and I'm not smart enough to understand your explanation of why that would work. :scratch:
But I'd like to know what results you get...
 

dbf909

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Essentially the 832 is the opposite of the 823 - the triodes have switched places. In the amp, there are 4 total gain stages in the preamp - 2 each for V1 and V2 and when in Red mode, they are all cascaded together - one after another - before the tone controls. The two triodes/stages that are switched in for the Red channel are the second side of V1 and the first side of V2. The functions of the triodes/stages (Green vs Red) are swapped between the V1 and V2 tubes. So in theory, an 832 should have the same effect in V2 as the 823 in V1.

It would definitely be easier to visualize with a drawing but somewhat difficult to describe in words.

How does it (ECC823 in V1) work for you? Does it drop the overall gain of the Red to a more useable level?

I've read that they basically implemented the equivalent of the "Lead 2" circuit as the Red channel in the 20.

Honestly, I would love to get the Red channel dialed in to approximate the "Crunch" mode on my DSL50...
 

Jon Snell

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Few people realize the the ECC83 has a higher gain and usually quieter 2nd stage. Pins 6,7 & 8 is the higher gain side. That is why all manufacturers back in the 50s, 60s and early 70s wired the higher gain side as the 2nd stage.
Newer JJs and other lower ranked Chinesium ECC83s do not have that option, that is why so many are looking for NOS Mullards and the like.
It is easy to check the gm with my AVO 160 characteristics valve meter.
 

Pete Farrington

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Few people realize the the ECC83 has a higher gain and usually quieter 2nd stage. Pins 6,7 & 8 is the higher gain side
Where have you got that from?
Philips note that with regard to hum, the 6,7,8 section is more favourable when arranged for a 6.3V balanced heater supply. From that, I suppose they mean hum somehow coupling into the triode from the heater.
But I’ve not seen anything about any other inherent difference between the two sections.
 

fitz

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How does it (ECC823 in V1) work for you? Does it drop the overall gain of the Red to a more useable level?
I would describe it exactly as you just stated.
Lowers the gain on the red channel.
Still way more than enough gain on 10 (imo) and more control on the lower end of the dial.
 

dbf909

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Cool thanks. Yeah that is pretty much what I am looking for. I haven't had a chance to look through my box of tubes yet. Hopefully tonight.
 

dbf909

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I found a couple of boxes - one with a bunch of EL34 type power tubes and another with a bunch of preamp tubes. Unfortunately, I did not find a 12DW7/ECC832 or an ECC823 in either box. So I went ahead and ordered one of each from Eurotubes. They should be here early to mid next week.
 

dbf909

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I got the two JJs from Eurotubes in the mail yesterday - super fast shipping.

I had a chance to spend an hour or so with it tonight. I started with all the stock tubes in the amp (Marshall branded JJs in V1 and V2, Marshall branded Shug in V3, Marshall branded JJ EL34IIs in V4,V5)... Swapped out the stock speaker with a well broken in UK G12M Greenback.

Guitar was a Gibson Les Paul R9 '59 Ltd Custom Shop Reissue with stock Custombuckers. I didn't have an opportunity to try a Strat or Tele yet - just trying to set a baseline with the Les Paul.

I first tried the ECC823 in V1. The Green channel got a little bit louder/gainier and quite a bit brighter I had to basically turn the treble off and the Presence to 8:00. The Red channel was noticeably less gainy but quite a bit darker as well. Not bad overall though - definitely in the direction I want to go.

So second, I put the original ECC83 back in v1 and tried the ECC832 in V2. Very little change in the Green channel - I could run the Treble at 10:00 and the Presence at 9:00 for a nice chimey clean tone. The Red channel was definitely lower gain but nowhere near as dark as with the ECC823 in V1. I definitely prefer this tube in V2. A bit more useable Gain setting and although still on the high end of what I consider "Crunch", it is far closer the the Lead1 channel on my DSL50.

So from here, I started rolling other tubes through V1. I stayed with 12AX7/7025/ECC83 types but tried quite a few. Started with 3 different Mullard RI, 3 different TungSol RI, Electro Harmonix, Sovtek WA and LPS (all new production Reflektor). Although they differed in subtle ways, they were all very bright in the Green channel and great in the Red channel. Some were more gainy and some less - I've never been a huge fan of these tubes in Marshall amps. They sound fantastic in Fender amps.

JJs on the other hand I think sound really dark in Fenders but can be great in Marshalls. So I tried a few JJs I had including an ECC83S Gold pin. Honestly, none of them sounded as good as the stock Marshall branded JJ.

I then tried a few other older (new production) tubes including an EI and a couple of older TADs and Groove Tubes. Even a Peavey branded 12AX7 that I found. Again some of them were slightly better than others but none beat out the stock V1.

So then I moved on to the NOS and older used tubes. I found some older RCAs, Sylvanias, GEs, Amperex, and a Blackburn Mullard. I have no way to know for sure if any of them are actually NOS since I didn't purchase them new back in the day so I assume they are used. However, they all test very strong and sounded great in other amps. Both of the RCAs were great on both the Green and Red channel but the clear winner was the Blackburn Mullard. It allowed the most use of the Treble and Presence controls on the Green channel and produced a really nice Marshally clean tone. And the Red channel was crunchy with a nice slightly darker tone but not too dark. I'm not great at articulating all of these things but that early 60's Blackburn Mullard in V1 was definitely the best with the ECC832 in V2.

I played it this way for about 15-20 minutes at different volume, gain, and tone settings and it is a good step in the right directlion. I then put the stock tube back in V1 and went through some of the same settings to see if the Mullard was really better - it was.

So I was getting a bit tired and there are quite a few combinations I'd still like to try. For instance, how about going back to the ECC823 in V1 and the Mullard or a few others in V2. I only tried this with the stock tube in V2 and didn't like it as well but who knows. Also, Id like to try a few lower gain tubes like a 5751 or a 12AY7 in V1 with the ECC832 in V2. I've got quite a few RCA, GE, etc NOS 12AY7s and 5751s in the box. It might just take enough of the edge off the Green channel as well as drop the gain a slight bit further on the Red channel.

I know in the end there is only so much you can do with tube swaps but it is interesting to see/hear the results of different combinations.

For now though the bottom line is that the ECC832 in V2 works better for me than an ECC823 in V1. More to come...
 
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dbf909

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Followup on my journey with the DSL20CR...

An RCA 5751 in V1 with the ECC832 in V2 is about as good as I can get with the tubes I have available in balancing out the Clean and Drive channels. However, even with this combo, I am still left wanting a little less gain on the Red channel and a little more on the Green channel.

So my ultimate conclusion was that I was probably too hasty in my sale of the DSL40c. And coincidentally (supporting this conclusion), another used one in mint condition revealed itself to me so I went ahead and bought it. Like the original 40c I had and sold, this one also has the Creamback speaker in it which sounds awesome. Yes it is still 53 lbs in that configuration but I will just use my foldable hand truck when I need to move it. I can't throw 50 lbs around like I used to 30 years ago... I put a Neo Creamback in it which dropped it to about 49 lbs and so far I love the tone of the Neo. It just reinforced that I love the Green channel for both Clean and Crunch. I will have to look at modding it to add footswitch capability for the boost.

But since then, I also came across an Origin20c used so I bought it as well. Obviously a very different amp than the DSL but they complement each other well and work great as a stereo rig. The Origin20c at under 30 lbs with a Greenback 10 in it works out well for a grab and go if I need to take a single combo for a jam or practice. So now I'm working out my pedalboard to optimize for the Origin20c. So far the Timmey, Klon, and RAT sound pretty good. However, so does the SD-1, and the Blues Driver, and the TS-808, and the MXR Distortion+. Damn, another rabbit hole... And I found yet another rabbit hole in rolling tubes for this one as well.

So in the end, the DSL20CR, while a great amp with some fantastic tones in it, was just not the best amp for me. The DSL40c, although heavier, is just more flexible. I love tweaking and messing with these things but it seemed that I was trying to make the DSL20CR into something that it was just not designed to do. Again, great amp - I loved what it does. Cost and portability aside, in this case it seems that the combo of the DSL40c and the Origin20c fills all the gaps that I had with the DSL20CR.

So the DSL20CR moved on to someone that will love it and I will enjoy my DSL40c and Origin20c...
 

Gene Ballzz

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@dbf909 ,
Though you alluded to wanting to try it in an earlier post, I don't see that you ever "actually" tried the combination of ECC823 in V1 and ECC832 in V2? Too bad that the DSL20 has "moved on" to another home! I guess if I want this question answered, I need to buy two tubes?

FWIW, the dichotomy of the whole DSL lineup has always been a tonal disparity between the two channels, making channel switching on the fly, a bit less than optimal!

Thanks,
Gene
 

dbf909

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Hi @Gene Ballzz ,

Sorry, I totally forgot to mention that I did get a chance to try the V1/V2 combo with both the 823/832 tubes. Thanks for the reminder on it. The result was that the Green channel was more or less unchanged - basically no different than rolling another 12AX7 in V1.

The effect on the Red channel was significant though. I was hoping for another equivalent drop in gain over using just one or the other. And the gain was definitely reduced. However, the tone got very dull and thin (if you can imagine both of those at the same time) and it really lost the essence of the amp. Messing with the tone controls helped a bit. I was really looking to (re)create the Crunch tone on the DSL40 and this combo did not do it. I think that reducing the (triode) mu of both of the switched in intermediate stages with these tubes is just too much.

I'm pretty sure that tweaking some of the other resistor and possibly capacitor values in the Red channel circuit would bring some of this back but just doing the tubes alone did not produce what I was hoping for. And modding the circuit was really out of the bounds of what I was interested in doing - especially when another DSL40c came along. I look at that as fate... It made my decision easier at least.

So from my (somewhat brief) experience in trying this, I can't really recommend subbing BOTH V1 and V2 for the ECC823 and ECC832 tubes at the same time.

As always, your mileage may vary... It was definitely worth the effort to try - gaining knowledge of what doesn't work is sometimes more valuable than what does work.
 
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Gene Ballzz

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Hi @Gene Ballzz ,

Sorry, I totally forgot to mention that I did get a chance to try the V1/V2 combo with both the 823/832 tubes. Thanks for the reminder on it. The result was that the Green channel was more or less unchanged - basically no different that rolling another 12AX7 in V1.

The effect on the Red channel was significant though. I was hoping for another equivalent drop in gain over using just one or the other. And the gain was definitely reduced. However, the tone got very dull and thin (if you can imagine both of those at the same time) and it really lost the essence of the amp. Messing with the tone controls helped a bit. I was really looking to create the Crunch tone on the DSL40 and this combo did not do it. I think that reducing the (triode) mu of both of the switched in intermediate stages with these tubes is just too much.

I'm pretty sure that tweaking some of the other resistor and possibly capacitor values in the Red channel circuit would bring some of this back but just doing the tubes alone did not produce what I was hoping for. And modding the circuit was really out of the bounds of what I was interested in doing - especially when another DSL40c came along. I look at that as fate... It made my decision easier at least.

So from my (somewhat brief) experience in trying this, I can't really recommend subbing BOTH V1 and V2 for the ECC823 and ECC832 tubes at the same time.

As always, your mileage may vary... It was definitely worth the effort to try - gaining knowledge of what doesn't work is sometimes more valuable than what does work.

@dbf909 ,

Thanks for sharing that info! And FWIW, that last sentence of your reply shows a wonderful observation and understanding of some of the finer aspects of reality.

Thanks Again,
Gene
 

mike58

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Did you get a read at my thread looking at DSL5c ?

I dont know if the DSL20CR has a phase inverter valve, but changing that for an ECC81 tranformed the harshness in the amp
Once I got my Goldilocks spec right the amp was gifted to a friend but I was so impressed how good the little DSL5c could sound I bought another 2 and tweaked then similarly and use them as a stereo rig. One on green cranked and one on red low/mid gain through a Marshall EH-1 stereo out delay on analog , tape echo, or modulation delay setting gives a massive sound with the delay set very subtle.
The EH-1 Echohead is a very cheap excellent sounding delay … and it a Marshall !!!
 


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