Thoughts on 100k plate amp, #124, and my Clone

[ic-racer]

"The best of its kind I've ever heard, absolutely no traces of harshness or otherwise "ugly" breakup to be found. "

Ayan Gill, referring to #124

So, I went ahead and converted my preamp components to match the values of #124 to see what it would sound like (BTW I thought the amp sounded pretty good before this). This basically meant converting the plate, cathode and grid resistors to the appropriate values. So now it is nearly identical to #124, both cosmetically and by schematic.

Overall it sounds way too bright. All my amps sound bright, but the frequency losses in the recording process make them sound OK on recording. This amp, however, even sounds bright and thin on the recordings.

There have been many posts on getting a good sound from a 100k amp, and my Fender Super Twin conversion has 100k and has been tweaked (thanks to this forum) to a super sounding amp.

So, I'm NOT asking in this post "how can I tame this amp." What I did want to bring up was a discussion of how an amp can be built as close as possible to the original, yet sound so different? What's the 'magic' that is missing?

Possible explanations for the difference between #124 and my amp that I was thinking of were:

A) Output transformer not exactly the same
B) Unknown key values?? ie components other than the 500k trimmer that are not 'as marked'
C) Improper build
D) Error in #124 schematic
E) Voltages different
F) Still a few minor deviations from #124 (eg 470p vs 500p cap)
G) Maybe its not all that far from #124 sounding after all?
H) Carbon Film Cathode resistors?
Others???

Voltage Comparison
#124
6L6 Plate 440v
V1 190v
V2 200v

My Amp
6L6 Plate 453v
V1 196v
V2 199v

OD entrance:
#124 220k into 345.5k trimmer set to 100k
My amp: 220k into 347k trimmer set to 96k (set by ear, then measured).

Posted for comparison, my schematic (which also has the #124 values) and the #124 schematic.

My soundclips as the amp stands right now:
http://soundclick.com/share?songid=6564934
http://soundclick.com/share?songid=6564969

[bluesfendermanblues]

excuse my studip question: what is a 100k amp??

[bluesfendermanblues]

I've listened to your two sound clips. ..it is a bright sound, but hey it sounds like albert king or freddy king. Its a nice characterfull blues sound, on the bright side, but cool.

The voltage figures that you mention are not an issue, they are within a range that will not affect sound significantly.

You must have misread a component value somewhere....and there is a number of opportunities. One could be the value of the slope resistor (should be 150k), which really impact the bhightness/darkness of the amp. However, it just one possibility.

Anyway, your soundclips are way cool !!!

[ic-racer]

excuse my studip question: what is a 100k amp??

An amp that has a 100k plate resistor on the 12AX7s in the preamp. Also, this would include 1.5k cathode resistors as well. These are Fender and Early Dumble values.

[odourboy]

You might add 'Dumbleator' to the list. In my (albeit limited) experience with Dumbleators, they attenuate the highs if you don't use the brite switch or compensate in some way. Then add in the effect of long cables - it's been mentioned more than once on this board that there was a long cable in the loop for this clip or that.

Question for Gil (or someone familiar with his typical 100K setup... ), what do you use in your loop?

[bluesfendermanblues]

Thanks, for infor regarding "100k" - I'm new on the forum and pretty much a novice in regards to Dumble amps.

However, I have build soldano (x88 pre), marshall (jtm45), fender (twin, bassman 59), mathless (dc30)and boogie (mark I & III) clones.

I was not aware that the 100k/1.5k would have a particaly sound. I thought it only related to the amount of gain to be achieved.

Anyhow, in regard to the debate that IC-racer what to initiate, I would suggest - given that the values in the two schematics/constructions are identical- that capacitor TYPE is pretty important in regards to tone in an anp.

Just for fun I replaced all the orange drop 716 caps in by bassman 59' with Sozo "mustard" caps of the same value and the amp changed from bright to mellow/dark.

And I tell you that I have som nice stuff in that amp Mercury Mag output transformer, GE NOS 6L6 output tubes, mullard preamp tubes, weber speakers. Perhaps this (the transperancy due to quality parts) is why a small change like capacitor type has such a major impact on tone ??

[bluesfendermanblues]

Thanks, for infor regarding "100k" - I'm new on the forum and pretty much a novice in regards to Dumble amps.

However, I have build soldano (x88 pre), marshall (jtm45), fender (twin, bassman 59), mathless (dc30)and boogie (mark I & III) clones.

I was not aware that the 100k/1.5k would have a particaly sound. I thought it only related to the amount of gain to be achieved.

Anyhow, in regard to the debate that IC-racer what to initiate, I would suggest - given that the values in the two schematics/constructions are identical- that capacitor TYPE is pretty important in regards to tone in an anp.

Just for fun I replaced all the orange drop 716 caps in by bassman 59' with Sozo "mustard" caps of the same value and the amp changed from bright to mellow/dark.

And I tell you that I have som nice stuff in that amp Mercury Mag output transformer, GE NOS 6L6 output tubes, mullard preamp tubes, weber speakers. Perhaps this (the transperancy due to quality parts) is why a small change like capacitor type has such a major impact on tone ??

[ic-racer]

I was not aware that the 100k/1.5k would have a particaly sound. I thought it only related to the amount of gain to be achieved.

At least with the Dumble topography, there is a significant change. This was my amp with 180k and 120k plates on the OD tube. : http://soundclick.com/share?songid=6455534

The 'series resistance' changed also, so that is accounting for some of the change in tone also.

[ic-racer]

I am inferring that Ayan's 'stock' #124 build was also too bright as he did these mods. I suspect a lot of these will work for me also, but I am trying to get ideas on why duplicates of #124 don't sound like the original.

1. Start with the schematic for ODS 124
2. I use a 100K pre OD trimmer (VS 350K trimmer)
3. I did not include the "brightness network" (220K//250pF) in the FX loop
4. I used a 30pF brightness cap on the amp's master volume, not 15pF
5. I used a 100KL "level" pot, not 250KA
6. I put a treble gate/tone control at the output of the OD, from the input of the 100KL "Ratio" control to ground. It has a 1,000pF cap in series with a trimmer (variable resistor). Setting is around 150K to ground or so
7. I use 5.1K grid stopper resistors and 1K 5W screed grid resistors on the power tubes
8. I use EL34s in this amp, at least at the moment
9. I use Marshall-style iron in my amp

[jaysg]

I recall Billy (or Gil?) talking about #124 vs. #124 clones. The amp was very well documented, however, in their opinion, none of the clones were anywhere near as good as the original. That pretty much leaves you with iron as the intangible. If HAD got an out-of-spec OT, he worked around it.

My notes say it was built in 1984. If he used the 1984 twin reverb set, it would probably be the set in the Twin Reverb II. I have an '83 Concert. Its universal 50W OT did not have the magic when used as a blackfaced amp. I replaced it with an Allen, which has the right stuff. A lot of conjecture here, of course. He could have pulled a silverface set....who knows. When you buy a Twin Reverb set today from any vendor, I think you're getting a well done blackface era pieces.

Since you're using Marshall 100W parts, all bets are off.

[edit] To Gil, below re: point #4 I recall/read Billy's comments to infer that he had heard more than one amp based on 124.

[ayan]

I am sure all I will write here can be searched for and found in previous posts, however, I can summarize the following:

1. Dumble ODS 124 sounded great. Very smooth, brown, non harsh. Not-a-clean-sound-in-it type of amplifier, however. I heard it before Billy recapped and retubed it, I don't know what it sounds like now.

2. I am not sure I could have commented on clones of it, since I really haven't heard clones of it besides my own 100K amp.

3. Billy's clone was close, construction-wise, to the original in that he used old Fender iron (Twin Reverb). However, Billy's amp used different parts (including yellow cylindrical caps that, to the best of my knowledge, Dumble never used) and did NOT use a true Skyliner EQ. I never heard that amp.

4. Perhaps the term "clones" was intended to refer to Dumble clone amps, generically, not clones ODS #124 specifically?

5. Quite frankly, my 100K amp has turned into my favorite amp of all time of all the ones I have ever played (regardless of who made them). It was up for sale for a while, before I had ever played live with it, and I am glad the deal fell through. I spent a day matching tubes to the amp and since then, the thing is nothing short of amazing. My desert island amp today. Before being turned into a 100K amp, it was a higher plate Classic, then a higher plate Skyliner amp. It didn't shine until the last conversion.

6. My 100K amp is very present sounding. I have described it as sounding like a harpsichord and have said that it is not intended for living room playing. It likes to be played loud and in a band context. And under those circumstances it truly is an "OMFG" amp. I am not one to toot my horn too loudly, so take my description with a grain of salt, but not a very big one. I have done two gigs with it to date and both times I have been blown away by its tone and have had people approach me to tell me that thing is out of this world. In one gig, I had a friend (Michael Sims, who lurks here and plays pretty good -- he's excellent, a pro guy) come and sit in. I lent him my rig and had a chance to listen from the audience... Unreal.

7. The amp reminds me of a couple of things: RF's TTYD tone for higher gain settings and something like vintage LC on a Princeton Reverb, as in "Chain Reaction" by The Crusaders, with less gain. Much chimier than anything with high plate load values on it and more prone to feedback as well. Doesn't sound like a violin/viola/cello/contrabss/etc. at all.

8. In it, I used the most economical iron I have ever used for any of my amps: New Sensor Corporation generic Marshall-type transformers. I would say that the NSC stuff is great, and that the Magic Parts TF-170 Marshall style OT is great too. As per my limited experience, the fabled Heyboer Twin style OT comes in a not too distant third.

9. If you built this amp, tweak it a bit. Choose the right tubes for it and get the PI balance to give you some extra love -- sweet spot varies, but a rule of thumb is getting the PI plates within 5 volts of each other or roughly so, higher on the non inverting side. Then take it to a real gig. You may be in for a surprise.

Hope this helps. Cheers,

Gil

[ic-racer]

Thanks for summarizing all this.

1. Dumble ODS 124 sounded great. Very smooth, brown, non harsh. Not-a-clean-sound-in-it type of amplifier, however. I heard it before Billy recapped and retubed it, I don't know what it sounds like now.

I suspect that the 'static' voltages don't tell the whole story. That is, under load, with the old caps, the voltages are lower. Or at least that is how I am understanding why my amp does not have the brown characteristics you described for #124, pre-capping.

2. I am not sure I could have commented on clones of it, since I really haven't heard clones of it besides my own 100K amp.

You must have thought about why your own #124 clone amp needed those deviations from #124's schematic? Or, did you use Marshall iron from the start, and just figure you will need to tweak it?

[ayan]

Thanks for summarizing all this.

1. Dumble ODS 124 sounded great. Very smooth, brown, non harsh. Not-a-clean-sound-in-it type of amplifier, however. I heard it before Billy recapped and retubed it, I don't know what it sounds like now.

I suspect that the 'static' voltages don't tell the whole story. That is, under load, with the old caps, the voltages are lower. Or at least that is how I am understanding why my amp does not have the brown characteristics you described for #124, pre-capping.

2. I am not sure I could have commented on clones of it, since I really haven't heard clones of it besides my own 100K amp.

You must have thought about why your own #124 clone amp needed those deviations from #124's schematic? Or, did you use Marshall iron from the start, and just figure you will need to tweak it?

Yes, old caps (and tubes) will maker amps sound way browner.

I probably commented along the lines of "My clone sounds nothing like ODS #124," as it doesn't. After all these months, once again, I like the sound of my 100K clone better for what I do.... But, I didn't reach that verdict until I spent some time finding tubes the amp liked.

Gil

[glasman]

Gil, you have me thinking I need to reinvestigate that 100W marshall iron I have sitting on the shelf. .

[ayan]

Gil, you have me thinking I need to reinvestigate that 100W marshall iron I have sitting on the shelf. .

Yeah man, FedEx ground will do nicely, You have my address.

Wait.... is that not what you meant?

Gil