100K Plate Amp (non HRM Findings): The Verdict

[ayan]

I took the amp out and played it with the band. Guitar used was my 335, amp's internal trimmer set to 30K to ground and settings from left to right: Volume 11 o'clock, Treble 11+ o'clock, Middle 11 o'clock, Bass 10 o'clock, Level 9+ o'clock, Ratio 1 o'clock, Master 1 o'clock, Presence 2 o'clock. This amp is outfitted with EL34s, has about 480VDC on the plates and is biased at about 34mA quiescent current. I plugged straight into the amp (no pedalboard this time around) and through my trusty D-lator clone and Intellifex. The amp is basically like #124 without the network across the FX loop, with my 250K + .001uF post OD treble bleed circuit (which I set about at 30% to ground on this amp) and with a 30pF brightness cap across the master volume.

The verdict? The amp just rips. I had reported the cleans were great and clean + PAB were also extremely musical, but this time around I stayed on the OD channel just about all the time. With the guitar volume low, the amp is clean. When turning up the volume on the guitar the amp can do one of three things: if you hit it soft, it will be clean and bright, percussive and piano-like; if you hit it a little harder, the tone thickens up and develops a “halo around the notes” feel; and if you hit it harder still it screams and then defaults back to the thicker sound (this phenomenon is the infamous chirp we usually talk about).

What was muddy and ice picky at home is simply excellent live, just like Dominik had written before. Probably not as good at “crunch” as the 200K/150K circuit, as the sound is thicker and punchier, but this is the best bridge pickup LC sound I have coaxed out any of my amps. Think along the lines of “Friday Night Shuffle” off Sapphire Blue, you can spoon out the tone.

I didn't try higher gain settings than those described because those settings sounded just too terrific and I couldn’t get enough of them. The boost on the OD sounds great too, and although brighter, just right for a band situation. I think this amp is sort of a missing link between the earlier 80s circuit (very easy to play, good crunch with OD, and screaming leads with OD + PAB) and the low gain HRM sound. Initially, it's not as friendly to play as the early 80s until you get a handle on the response of the amp, but then it really does the lower gain thing better. Lastly, this amp begs to be played loud.

I will have to try a Strat and a Tele too for completeness, but the amp is a keeper for the 335 alone, if nothing else. Still believe the 220K/150K amp (and w/.047 mid cap) will continue to be the ticket for the Strat. Next build (in progress) will be a BM, just because I have to build one and hear it. However, if it sounds any better than this amp, it will simply be a tone monster. I will post a couple of shots of the modded amp in the files section later.

Cheers,

Gil

[talbany]

Gill
Thanks for posting your findings. I am building an HRM for Rick Derringer 100 watts he plays pretty much OD most of the time. He uses his Warrior
model with P-90's. would you recommend the 100k/1.5 for the 90's he likes it smooth violin like tone. Looking foward to the shot's


Tony VVT

[odourboy]

Really exciting stuff Gil! (esp. since I'm getting organized for a non-HRM project when I finish my Funk build)

A couple of questions:

Is you Level (OD drive) pot a linear or audio taper (want to make sure which "9+" o'clock)?

What sort of cab/speaker did you use with this setup?

I was also interested in your thoughts on this proposal from your other thread (specifically, the 100Ks clean and higher on the OD):

Would going to 180k/120k on CL1/2 and then having the 220k/150k on OD1/2 (all with the 'corresponding' Rk values) be any sort of happy medium?

I was thinking the same thing, only with the 100k on CL1/2 and 220k/150k on OD1/2.

Cheers, Brian

[jelle]

Congrats!
This is exactly what I found too. And yes, I like it loud too!

[TimS]

Thanks for the report.

Man, between this and all the talk about the BM circuit, I don't know where to begin. They all just sound so good.

[ayan]

Here are answers to the questions asked:

1. I have no experience with either P-90s or violin tone. I would be inclined to believe the higher plate loads would be a step in the right direction, since the sound tends to be smoother and more compressed that way.

2. Level and Ratio pots are both 100KL.

3. I use either a 1x12 open back EVM12L (200W) cabinet, or an oval back 2x12 with two Eminence M12-8 (I think that's what they are?), which sound a bit kind of like the Celestion Black Shadow 90Ws (Boogie label).

4. I will not change this amp at all -- at least not for now-- so I guess I won't be finding out about 100K for the clean section and higher for the OD.

5. The cleans in this are are way better than in the higher plate load non-HRM amps -- real world fact, anyone that says different is just plain wrong.

Cheers,

Gil

[TimS]

the earlier 80s circuit (very easy to play, good crunch with OD, and screaming leads with OD + PAB)

I don't mean to derail the thread, but could you please describe what this circuit consists of? I haven't had any luck finding it on this site or any other for that matter.

[ayan]

the earlier 80s circuit (very easy to play, good crunch with OD, and screaming leads with OD + PAB)

I don't mean to derail the thread, but could you please describe what this circuit consists of? I haven't had any luck finding it on this site or any other for that matter.

What I call the early 80s amp is similar to the Skyliner, but with a few important differences. Schematic is not out because there are not that many of those amps around that have not been "upgraded" to either Skyliner of HRM, and because the earlier schematics have been kept underground at the orginators' request. But, I can comment on the differences between that and say something along the lines of #124:

1. 220K/150K plate and 3.3K/2.2K cathode resistors for both V1 and V2.

2. V1A grid stopper is 22K, as opposed to 33K for the 100K amp.

3. Tone stack has a .047uF midrange cap.

4. Bass and middle tone pots are 250KA (no .001uF cap across it) and 100KL, respectively, and the tail on the bass pot is 1K, not 10K.

5. Deep Switch instead of Mid switch. The Deep switch, if you have not tried it, is very nice: it adds a bit of bass to the sound, tames the highs slightly and, best part, is that it also tames down the PAB mode. In contrast, I have found the Mid switch to have a lot of limitations.

Gil

[JimiB]

what about the cathode bypass caps?

[TimS]

the earlier 80s circuit (very easy to play, good crunch with OD, and screaming leads with OD + PAB)

I don't mean to derail the thread, but could you please describe what this circuit consists of? I haven't had any luck finding it on this site or any other for that matter.

What I call the early 80s amp is similar to the Skyliner, but with a few important differences. Schematic is not out because there are not that many of those amps around that have not been "upgraded" to either Skyliner of HRM, and because the earlier schematics have been kept underground at the orginators' request. But, I can comment on the differences between that and say something along the lines of #124:

1. 220K/150K plate and 3.3K/2.2K cathode resistors for both V1 and V2.

2. V1A grid stopper is 22K, as opposed to 33K for the 100K amp.

3. Tone stack has a .047uF midrange cap.

4. Bass and middle tone pots are 250KA (no .001uF cap across it) and 100KL, respectively, and the tail on the bass pot is 1K, not 10K.

5. Deep Switch instead of Mid switch. The Deep switch, if you have not tried it, is very nice: it adds a bit of bass to the sound, tames the highs slightly and, best part, is that it also tames down the PAB mode. In contrast, I have found the Mid switch to have a lot of limitations.

Gil

Thanks. So it's basically a '70s non-HRM with the higher plate/cathode resistors?

[dogears]

The "grail" 80s amps I have heard of or seen, have had either 10uf or 25uf on both triodes of V1. Not 4.7uf. This is a big deal as prior opinions of the 100K amps was based on 4.7uf there. With 4.7uf caps, the 100K amps had a reputation for a bit bright and thin.

what about the cathode bypass caps?

[mlp-mx6]

Next build (in progress) will be a BM, just because I have to build one and hear it.

Gil, I'm stoked that you're building again. You've helped all of us so much, I'm glad your soldering iron is back in the game!

Michael

[heisthl]

with my 250K + .001uF post OD treble bleed circuit (which I set about at 30% to ground on this amp) Gil

SO a .001 in series with 82k(+/-) to ground after the CC on OD2?
I'm suprised that doesn't hurt the gain of the stage....IMWTK

[ayan]

with my 250K + .001uF post OD treble bleed circuit (which I set about at 30% to ground on this amp) Gil

SO a .001 in series with 82k(+/-) to ground after the CC on OD2?
I'm suprised that doesn't hurt the gain of the stage....IMWTK

1. That is not quite right: the treble bleed arrangement is connected AFTER the 150K resistor that comes after the CC on OD2. Hardly any loading at all, even if you put the trimmer all the way on the ground side -- and still, any loading would hurt volume not quite gain at that point.

2. As far as "building again," I had built two amps last year -- sold everything else I had. I did take a hiatus between something like 2004 and 2006.

3. Yes, the early 80s is kind of like a 70s amp but with higher plates and cathode resistors and the 220K resistor before the 100K trimmer at the input of the overdrive.

4. I have it on pretty good authority that back in 1982, RF's amp looked just like I just described.

Gil

[odourboy]

Here are answers to the questions asked:

4. I will not change this amp at all -- at least not for now-- so I guess I won't be finding out about 100K for the clean section and higher for the OD.

Cheers,

Gil

Thanks for the answers Gil. On this one, I wasn't suggesting you change your amp, but rather, to speculate on how such a change might sound.

Anyway, it's one variant I might just have to try!

Cheers, Brian