HRM needs some Lovin'

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fred.violleau
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Location: Montreal, Canada

HRM needs some Lovin'

Post by fred.violleau »

Hey guys,

As a newby to this forum, I can't thank enough all the passionate peeps gathering and sharing all that information about these fabulous amps.

I got my hand on a build that needs some lovin'. It appears there are 2 Hammond Trannys. It came with 2 Fender RCA 6L6s and a messy single board.
From what I have gathered so far, it looks (and sounds) like a 40-50 watts HRM, with an attempt to add a reverb tank (which apparently never worked said the previous owner.).
The clean channel has the tone stack that does not operate normally (ie when turning the knobs, nothing changes much, subtle differences at best for Bass, mids and treble). It has a lot of punch and a bright quality to it. Th OD stack is probably more messed up, very raw in your face type of OD, very loud.
And the amp seems dead when the PAB is disengaged. Also it looks like Master Volume is bypassed when playing with the manual switches in the back (footswitch switches).

I decided I could try to:
1- get rid of the reverb attempt
2 - troubleshoot the tonestack
3 - troubleshoot the OD stack
4 - re-wire the damn thing properly (at least with the right gage)
5 - replace the reverb attempt with an on board D'lator.

Thoughts and advices are very welcomed

Here are a few pics if you can help me with the obvious, it would be greatly appreciated.
20170606_200440.jpg
20170606_200409.jpg
Thanks for the help, and I will document on this thread my evolution on this project.

Will try to post some sounds samples as well.
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10thTx
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Re: HRM needs some Lovin'

Post by 10thTx »

Honestly, if it were mine ...... I remove the chassis layout board & start over with Orange Drop PS caps and Vishay-Dale RN65 resistors on a new layout board. You might be able to keep the power supply board section?

And I'd have a good layout printed off in front of me as well as a good schematic. With respect, 10thtx
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xtian
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Re: HRM needs some Lovin'

Post by xtian »

Call it a study project. Print an HRM layout and schematic, and examine your amp point by point. Mark on the schematic everywhere there is a difference and what it is. That will give you an idea if you can fix it up, or tear it out and start fresh, like 10thTx suggests.

How does this amp sound, BESIDES the tone? I mean, is it quiet at idle, or is there a lot of hum?
I build and repair tube amps. http://amps.monkeymatic.com
fred.violleau
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Re: HRM needs some Lovin'

Post by fred.violleau »

@10thtx, That was my first plan. But as I improvise as an amp Tech, I thought I ought to take it slow ;) I am still struggling with the idea.. I thought the caps were Orange drops. Is there different types of orange drop?

@xtian, I have started to map all the differences. I Will post a pic of my work as soon as I can.

The amp is not as quiet as my prosonic, but it is decent. I will AB test my 2 amps to hear the difference.

Thks for all the advices, much appreciated!

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10thTx
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Re: HRM needs some Lovin'

Post by 10thTx »

I believe the Orange Drop 715 series are polypropylene & the PS series are polyester. They really do sound different & I think in a d-style amp that the PS series are MUCH smoother in my experience.

I like the OD 715 but more in Fender clean style amps like AB763 series.

I think taking it slow and one step at a time is reasonable. @xtian gave you some excellent advice.

with respect, 10thtx
ChopSauce
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Re: HRM needs some Lovin'

Post by ChopSauce »

Nice catch! Where did you get this?

Just to outline one of the excellent suggestions - above: troubleshooting the tone stack should be easier with a proper layout - & the adequate board, but maybe your board also conforms to one layout from here, beyond having been seemingly wired in the hurry?
fred.violleau
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Re: HRM needs some Lovin'

Post by fred.violleau »

@ChopSauce I got this on kijiji. Wired in a hurry is the least one can assume ;)

@10thTx thanks for sharing the wisdom of the components, It will save me time!

I spent last week going back and forth with differents layout measuring values of resistors on the preamp board and it looks to be a mix between a HRM and a bluesmaster with some fixing for the reverb part... I changed some pots as the values were way off.

I finally decided to redo the preamp board as there are too many components to remove and/or change. I ordered a kit of fiber boards from marsh amp and I will look for components this week.

I also want to put the OD internal tone stack on the back of the chassis. I was wondering if I needed to use shielded wiring (same as the front tone stack ).

Any advices on this?

Again thks for your time and wisdom!

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Last edited by fred.violleau on Thu Jun 29, 2017 1:18 pm, edited 1 time in total.
ChopSauce
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Re: HRM needs some Lovin'

Post by ChopSauce »

fred.violleau wrote: Mon Jun 19, 2017 12:37 pm I also want to put the OD internal tone stack on the back of the chassis. I was wondering if I needed to use shielded wiring (same as the front tone stack ).
I look forward to reading "the" answer (just out of curiosity) but I could see OD control pot wires shielded, so this makes one more reason to "shield the OD tone stack", too.
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M Fowler
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Re: HRM needs some Lovin'

Post by M Fowler »

Henry's Redplate Magic Dust Dual amp has a HRM OD and non HRM OD on the front panel and I've attached a photo which I believe it used shielded wire.

Mark
MDD guts.jpg
mdd_guts 5-19-2010.jpg
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fred.violleau
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Re: HRM needs some Lovin'

Post by fred.violleau »

@Mark, thanks for the pics, had not heard about these amps before. Great builds from what I see.

I have almost all the components and the fiber boards have arrived.
Spent quite some time drilling holes in the chassis to make room for the extra pots of the HRM tone stack.
I realised I need to shuffle things a little:
- move the footswitch plug in the back of the amp,
- move the jewel from right to left so I can put the HRM tone stack on the front of the amp
- move the speaker outputs left in order to accomodate a half power/full power switch and the footswitch plug (change the 5 pin switch for a stereo jack plug).
- drilled extra holes in the back of the chassis to make room for the C-lator.

I plan to work on the shuffling and the HRM tonestack this weekend. Will attack the tonestack fiber board if i have enough time.
Can't wait!
Cheers!
fred.violleau
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Re: HRM needs some Lovin'

Post by fred.violleau »

I am working on the footswitch, and was wondering if the .01 uf caps are needed? Are they are here to avoid pops when switching channels or do they have another purpose ?

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norburybrook
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Re: HRM needs some Lovin'

Post by norburybrook »

I've just finished a build and didn't use them. I'm not aware of any negative effect :D



Marcus
fred.violleau
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Re: RE: Re: HRM needs some Lovin'

Post by fred.violleau »

norburybrook wrote:I've just finished a build and didn't use them. I'm not aware of any negative effect :D



Marcus
Thanks for the feedback Marcus. Cheers!

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fred.violleau
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Location: Montreal, Canada

Re: HRM needs some Lovin'

Post by fred.violleau »

A little update of my whereabouts:
-Cut off the fiber board and removed the original layout board.
-sanded all the edges and make sure I did not damage anything in the meantime.

Next step : recycling some of the old components for the new layout board .
ImageImageImageImage

Fred, learning everyday!


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norburybrook
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Re: HRM needs some Lovin'

Post by norburybrook »

that's more like it :D

M
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