A/B test and a question

[Luthierwnc]

Hi guys;

This morning I had a chance to air out both of my 50 watt heads with Mike Barnes, a great local player. One amp is the following:

HRM with JTM45 Iron and JJ KT77's at around 455 VDC on the plates. MPP caps, high plate resistors, modern power filters. There is an internal Dumbleator. No FET but it does have the 150k on the end of the rail. Pots, resistors and caps are all as per the usual schematics. Bright, deep and mid but no R/J. RN65 resistors in all plate supply points. Assorted elsewhere. Assorted former Soviet Block preamp tubes. 1k screen resistors

The other is based on the Grail Tone schematic using Fender Iron and TAD 6l6GTC's. Same types of preamp tubes as above. RN65 power resistors, orange drop PS couplers, external D-lator, switchable NFB on V1b (on in OD, N/C on clean). Skyliner tone stack (I also have my Strat switch for an older preamp version but we didn't use it for this test). No Fet. B+ around 450. Older-style power supply. I have Gil's treble bleed with the pot most of the way up. Both amps have a Ford/choke switch and we played them both ways. 500R screen resistors.

Mike played a 2 humbucker guitar with no pedals. I mostly fiddled with knobs. He played the HRM through two 1X12 open backed cabs with G12-65's to start and the non-HRM was through a Thiele 1X12 with an EVM-12L. Later, we put both amps through an EV. The amps weren't dimed but they were given a fair run through the volume settings. The D-lators were both set a little above parity. He had an A/B/C switch box with a DR attached as a reference tone.

We both had the overall impression was that the cleans on the non-HRM were the must-have tone. It was just better through the range. The HRM also has nice cleans but the mids were a bit too much at most settings.

The HRM won the day on the boosted and OD settings where those mids can be put to better use. They seemed to sustain better on lead playing and had the crunch with clarity. Both amps sounded really good and without the other one to compare, it would have been hard to find fault with either.

So now I am sitting here typing and looking at schematics trying to figure out how to get the best of both worlds. Adding the newer power section to the Grail Tone might create some space considerations -- as would an internal D-lator. I left room for an HRM sled when I did the board. My thoughts are just to swap out the high plates for low on V1 and lows for highs in the OD but I am sure there must be other considerations for how each will drive the next stage.

So here's the question: what have you done in your prototypes to combine the two technologies and get the better of each? Component suggestions are also welcome.

Thanks, Skip

[dogears]

Both amps have the same clean channel topography so your difference is the output. The KT77 are much middier....

[Pete]

I guess I'm not familiar with the "Grail Tone" schem, just to be clear (at the moment I'm assuming), this would be low value plate/cathode, correct?

I ask because my experimentation lead me to prefer the high values for cleans (using 100% 6L6).

My thoughts are just to swap out the high plates for low on V1

[Luthierwnc]

Thanks Scott,

Pete; Here is the file on that schematic:

https://tubeamparchive.com/files/early_ ... v0_353.pdf

It is a non-HRM model using the older power supply and .047 mid cap. The big differences in mine are that I used 100k plate resistors on the older style and the higher values on the HRM. The cleans are definately more Fendery but, in my case, the overdrive doesn't have the focus of the HRM. I built it so I could see which I liked and prefer the HRM but there is a lot to be said for aspects of this flavor.

Another thing I did differently was to have switchable tone caps and pots. One way it uses the Skyliner and the other has a 0.1/250k, 0.047/100k old-school stack. I have a thread called "Strat Switch". It worked out pretty well as an experiment, and the older way does work better for that guitar -- but not well enough to bother. With either stack, this is a bucker amp.

What I'll probably do is rearrange the real estate and put in the HRM power and V2 values and leave the first two stages alone. A Bluesmaster is also a possibility. It is a little more drilling and shifting than I had planned but these amplifiers must be obeyed.

sh

[Luthierwnc]

bump

I'm still fishing for an idea to tighten up the OD section of the non-HRM. I didn't mention it has 270pf snubbers. Another thing I didn't mention is that it has two OD relays. One is just like all the rest. The other is also a dpdt. One side controls the V1b negative feedback. A switch on the back panel allows: no feedback, all feedback or that the relay switch will engage it when the OD is on and disable it when the OD is off. The other side of that relay disconnects the bright switch when the OD is on.

My thinking includes the possibility of going with high-plate values in the OD and maybe unbalanced snubbers but it is a grope.

Keep those ideas coming in,

thanks, sh

[greiswig]

bump

I'm still fishing for an idea to tighten up the OD section of the non-HRM.

Hi,

I'm not sure what you mean by "tighten up." If you mean that the lows feel flabby, you've probably seen the (typically) .02uF cap into the OD section? On my amp, that didn't seem to be enough: by the time I got the lows in the clean side to be nice and full, the OD side was overwhelmed. IIRC, I ended up with a .01 entrance cap, but I also tinkered with lower-value cathode bypass caps that seemed to help a lot.

[jelle]

Do you have the 1uf cathode cap on v1b as per holy grail schem? I understand that that was used in one amp only and that this amp ended up in Japan. Or is it a 5uF? This changes the sound an feel a lot.

As for getting more focussed OD: you can change the entire OD section to HRM specs, starting from OD entrance to HRM tonestack and separate masters. That could be fun. If you like it, then I'd continue to the PS board.

Have fun!

jelle

[Luthierwnc]

I used 5's in all the cathodes.

In truth, it is probably just that I/we liked the HRM better when the hair was applied. Converting the non to that would be pretty simple. The power supply would be trickier because it is a donor chassis and not deep enough to use a totem pole arrangement. At least, I don't think so now but the amp is sitting on my foot stool in the library and I'll take some measurements tonight.

Back to one of my earlier posts, I made this amp as Strat-friendly as I could and it sounds really good. The cleans are the better of the two. What I'm wrestling with now is how to improve the OD without losing the great V1.

Thanks again for all who read, posted or thought about it. Cheers,

sh

[dave g]

This may be just me - but I have never liked 5uF bypass caps on CL1 and 2 on non-HRM amps whenever I've tried them. For me it's gotta be 10uF on both with a .047 CL2 coupler in order to get the fullness on the cleans. You can control the bass going into the OD by throwing in a series cap ranging from .01 to .05 in the OD entrance so that your effective CL2 coupling capacitance is lower in OD than when in clean.

Also, if you're using 180k on the grid of OD2, why don't you try dropping it to 150k (or lower). I know dogears swears by it...

[dogears]

I use the 150K grid on OD2 only on EL34 non Bluesmaster HRM amps. I always use the 180K on non HRM amps.

You can try something like 180K/120K on the clean plates on the HRM to get some more organic chimier cleans.

This may be just me - but I have never liked 5uF bypass caps on CL1 and 2 on non-HRM amps whenever I've tried them. For me it's gotta be 10uF on both with a .047 CL2 coupler in order to get the fullness on the cleans. You can control the bass going into the OD by throwing in a series cap ranging from .01 to .05 in the OD entrance so that your effective CL2 coupling capacitance is lower in OD than when in clean.

Also, if you're using 180k on the grid of OD2, why don't you try dropping it to 150k (or lower). I know dogears swears by it...

[dave g]

My mistake - I stand corrected!

[Luthierwnc]

Dave; I had a look and did put a 10 on V1a non-HRM. 5 on b.

greiswig: not sure which .022 cap you mean on the entrance. I've got a .047 coming off V1b. On this amp, my concern is that those great cleans are pushing the OD a little too hard. I can't say the bass is mushy. It might just be that I'm an HRM guy and had to prove it. Still, I'd like to give this amp a chance with the older architecture. There are so many things to alter that it could take a while. Perhaps some bigger plates in the OD (they are all 100k in this amp) and I can back off the entrance pot a hair.

Thanks Scott, I'll try the lower plates on the HRM - prolly drop the cathode resistors accordingly too. sh