New HRM build

[ic-racer]

I think all the HRM amps I've ever heard of had the trimmers wired the conventional way such that they worked "clowckwise." I hear you on the settings one sees out there, but I'll take that a step further and wonder why Dumble would pick a 1 Meg trimmer for the bass anyway? The on-off effect of the bass is much less pronounced if one uses something like a 250K or 470K trimmer and for me, the usable ranges were achievable with a 250K one. I don't thínk we'll ever get a good answer for this one.

Cheers,

Gil,

I have been wanting to ask you, did you ever twist the trimmers in someone's HRM to confirm which way they work?

Either way, I'm pretty happy with the sound I'm getting with it wired the way shown and set like the pictures. (see Youtube video above).

Again those settings may be only good on this one amp which is 220/150k, 220/150k with a little different voltage dropping string and some other differences from other documented HRMs.

[Structo]

The one HRM complaint I have heard over and over is the Bass trimmer is like an on/off switch.

It does seem strange to have a 1M trimmer there.
I've been thinking about putting a tone control on my OD.

Like a 5E3 tone or similar.

I have tried using the treble bleed type control but it seems to take too much off.

Good looking amp there Ic-Racer.

Sounds good as well.

[jlatrace]

Would you mind posting your voltages? I am starting on a BM HRM using Fender PT that will probably run at 450 vdc on b+ 1 (plates).

Great build, thanks for the pictures.
Les

[ic-racer]

Would you mind posting your voltages? I am starting on a BM HRM using Fender PT that will probably run at 450 vdc on b+ 1 (plates).

Great build, thanks for the pictures.
Les

Plates 448
Screen 446
Yellow 423
Purple 314
Red 306

Clean stage 1 plate 193
Clean stage 2 plate 202
OD stage 1 plate 202
OD stage 2 plate 213
V2 202

[Structo]

I assume you have a choke before the screen node?

What size screen resistors did you use?

For some reason my screen voltages are always the same as the plate voltages at idle.

May have to try the voltage divider method to see if I can drop them a couple volts.

[ic-racer]

I assume you have a choke before the screen node?

What size screen resistors did you use?

For some reason my screen voltages are always the same as the plate voltages at idle.

May have to try the voltage divider method to see if I can drop them a couple volts.

Power is Fender Twin style Hammond 290FX

My dropping string is :
3K 10W (big brown one)
22k 2W
2k2 2W

That is a little different from other HRMs out there and different from HRM-BMs. Those are, however, the values on the amp on which my build is based.

My screen resistors are 1k, 5W. Yes the screen is after the choke (Fender Twin Style, TF-155 style)

Again, for anyone reading this that has not read all the pages of the thread, the amp is a non-BM HRM with EL34.

[ayan]

I have not messed with any trimmers on any real amps. One thing, however, is that a lot of the HRM players out there use Celestion speakers which will generate a completely different frequency response than, say, an EVM 12L. I use EVMs and found the HRM amps hard to dial because I do not like a lot of bass and keeping the bass low in the HRM (say 100K to ground or so), required that the treble and mids be kept fairly low too, and that was not a good sound. Celestion 65s, for example, shave off a lot of the treble and bass, and may be friendlier with HRM amps.

Anyway, I have friends who have messed with the internal trimmers and none ever reported having them wired backwars. Furthermore, most reported that the amps sounded balanced with the controls about halfway up.

Regards,

Gil

I think all the HRM amps I've ever heard of had the trimmers wired the conventional way such that they worked "clowckwise." I hear you on the settings one sees out there, but I'll take that a step further and wonder why Dumble would pick a 1 Meg trimmer for the bass anyway? The on-off effect of the bass is much less pronounced if one uses something like a 250K or 470K trimmer and for me, the usable ranges were achievable with a 250K one. I don't thínk we'll ever get a good answer for this one.

Cheers,

Gil,

I have been wanting to ask you, did you ever twist the trimmers in someone's HRM to confirm which way they work?

Either way, I'm pretty happy with the sound I'm getting with it wired the way shown and set like the pictures. (see Youtube video above).

Again those settings may be only good on this one amp which is 220/150k, 220/150k with a little different voltage dropping string and some other differences from other documented HRMs.

[ic-racer]

Thank you for your comments Ayan.

I got an EVM 12S from Craig's list. I have a Thiele cabinet on order from Bludo for a few weeks now. Once that arrives I'll probably have to do some more tweaking.

[IMG:414:450]http://img.photobucket.com/albums/v670/ ... 581aaf.jpg[/img]

[stelligan]

HRM amps are my favorites but, it's kind of a love/hate relationship. Once they are dialed in, they are fantastic! Getting there can be painstaking and brutal(for me anyway). Still my favorite OD type. My first was skyliner - the one I am in the middle of now is bluesmaster.

Good luck with yours. Great thread and super looking build! Sounds very good already - just saw/heard the video. Super.

[pazzo63]

Ciao , i think 448 volts on the plates is a little low ,for HRM i would go for around 460 /465v on the plates instead .Best Wishes dd

[ic-racer]

Ciao , i think 448 volts on the plates is a little low ,for HRM i would go for around 460 /465v on the plates instead .Best Wishes dd

All the Fender Twin style power transformers I looked at all put out 640V. Do you know a Twin style transformer that puts out 690V?

[aflynt]

Ciao , i think 448 volts on the plates is a little low ,for HRM i would go for around 460 /465v on the plates instead .Best Wishes dd

All the Fender Twin style power transformers I looked at all put out 640V. Do you know a Twin style transformer that puts out 690V?

http://www.classictone.net/40-18042.html

I have one of these in my #102 clone and am getting between 465 and 470 volts on the plates using the 345-345 taps.

-Aaron

[ic-racer]

Ciao , i think 448 volts on the plates is a little low ,for HRM i would go for around 460 /465v on the plates instead .Best Wishes dd

All the Fender Twin style power transformers I looked at all put out 640V. Do you know a Twin style transformer that puts out 690V?

http://www.classictone.net/40-18042.html

I have one of these in my #102 clone and am getting between 465 and 470 volts on the plates using the 345-345 taps.

-Aaron

I missed that one, I guess I did not suspect they'd give that one a 690vac option and not the other one. Sure has a lot of wires coming and going

Maybe it was a mistake to go with the Hammond 290FX

[pazzo63]

Ciao yes classic tone i guess it s a better option than hammond, the voltages and the power transformer choice is a crucial factor for the best Dumble sound in my experience BEST REGARDS

[talbany]

It's really a kind of strange thing to me in that my BM HRM amp (which has the controls and OD trimmer all placed on the outside of the amp) can be a little difficult to dial in at times
I find myself wanting to tweak that thing every time I change guitars/rooms/ speaker cabs..etc
I don't seem to have this problem with my non HRM amps..Most everything I plug into it and no matter where I play it for the most part seems to balance itself out much better..Mine has a 500k bass pot and generally start out on my BM with bass and mids around noon and mid/ treble around 9:00 (Celestion 65's)..BTW I use a partial PAB boost and don't completely lift the stack..MY BM is a love hate amp!!

Tony