HRM needs some Lovin'

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didit
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Re: RE: Re: HRM needs some Lovin'

Post by didit »

fred.violleau wrote: Fri Aug 25, 2017 9:35 pm
didit wrote: See 1650HA OPT. Curious regarding the power transformer.
1650HA is the actual tranny used on this build.
Yep. Can't read the tag on the power transformer however...
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Re: RE: Re: RE: Re: HRM needs some Lovin'

Post by fred.violleau »

didit wrote:
fred.violleau wrote: Fri Aug 25, 2017 9:35 pm
didit wrote: See 1650HA OPT. Curious regarding the power transformer.
1650HA is the actual tranny used on this build.
Yep. Can't read the tag on the power transformer however...
It seems to be a Hammond 274 BX.Image

Fred, learning everyday!

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didit
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Re: RE: Re: RE: Re: HRM needs some Lovin'

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fred.violleau wrote: Sat Aug 26, 2017 8:40 pmIt seems to be a Hammond 274 BX.
OK. So roughly 500VDC with silicon rectification, so tad high. Over-robust for 6L6 conventions. Encourage D-style cognoscenti to advise.
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Re: RE: Re: RE: Re: HRM needs some Lovin'

Post by pompeiisneaks »

didit wrote: Sun Aug 27, 2017 2:15 pm
fred.violleau wrote: Sat Aug 26, 2017 8:40 pmIt seems to be a Hammond 274 BX.
OK. So roughly 500VDC with silicon rectification, so tad high. Over-robust for 6L6 conventions. Encourage D-style cognoscenti to advise.
Is that including the expected drop once the tubes are in? It seems to me at least with one (TAD) 6L6GC I see 500VDC as a max, and if you add in the drop the tubes will provide, it should be in range no?

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didit
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Re: RE: Re: RE: Re: HRM needs some Lovin'

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pompeiisneaks wrote: Sun Aug 27, 2017 3:34 pm Is that including the expected drop once the tubes are in? It seems to me at least with one (TAD) 6L6GC I see 500VDC as a max, and if you add in the drop the tubes will provide, it should be in range no?
Loaded, unloaded expect 550V or so.
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norburybrook
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Re: HRM needs some Lovin'

Post by norburybrook »

My wonderland is around 500c DC loaded on the plates with 4x JJ 6L6's. lovely sounding amp :D

Marcus
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Re: RE: Re: RE: Re: RE: Re: HRM needs some Lovin'

Post by fred.violleau »

didit wrote:
pompeiisneaks wrote: Sun Aug 27, 2017 3:34 pm Is that including the expected drop once the tubes are in? It seems to me at least with one (TAD) 6L6GC I see 500VDC as a max, and if you add in the drop the tubes will provide, it should be in range no?
Loaded, unloaded expect 550V or so.
Just to be sure I am following you, are you saying that the P.O.T. is too high for that kind of build?

Would it burn/damage the tubes faster if operating with current voltage? What would be the impact on the sound?

Would I be able to add a resistor to drop the DC voltage to an appropriate value?

I like the punch the amp had on the clean channel. It was too rough when adding the OD stage.

Also Mark convinced me too get a new chassis. After all, you only get one chance to do the right thing ;). My trannies are both mounted in an up position. Can I mount one of the two in a "lying" position? Can I change the mounting screws by myself ?

I have seen Wreck amps having both trannies mounted in up position, so would it change a lot for my build?

Thanks for the help.

Fred, learning everyday!


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didit
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Re: HRM needs some Lovin'

Post by didit »

500V DC works. Just somewhat higher than convention. May require a larger resistance at one or more dropping string nodes, starting with the first below the choke. Divider in the bias supply could need changes to get the trimmer correctly in range. There is lots of heater current (6A), so the flexibility to change up power tubes for KT77/KT88 or 6CA7. Upright transformers are fine. Some careful positioning might be needed to minimize noise. Looks OK as-is.

This will work. Not paint-by-numbers, so an opportunity to learn and lean on the knowledge & creativity here.

Best .. Ian
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M Fowler
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Re: HRM needs some Lovin'

Post by M Fowler »

It's a little bit high secondary voltage but you could run 6550 or KT88 for something different then the old run of the mill Dumble clones.
Use a tube rectifier 5U4 or 5V4 to bring secondary down if you want. Also, reverse zener diode on HT center tap say a 50v zener to bring it down approximately 45v.

I like upright PT mounting leaves lots of extra room in the chassis for other goodies.
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didit
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Re: HRM needs some Lovin'

Post by didit »

Zener or power FET variable works. Tube rectification & >100uF primary filter is complicating. Suggesting adjustment to dropping resistor(s) and consideration to beefy power tubes simplest.
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Re: RE: Re: HRM needs some Lovin'

Post by fred.violleau »

didit wrote:500V DC works. Just somewhat higher than convention. May require a larger resistance at one or more dropping string nodes, starting with the first below the choke. Divider in the bias supply could need changes to get the trimmer correctly in range. There is lots of heater current (6A), so the flexibility to change up power tubes for KT77/KT88 or 6CA7. Upright transformers are fine. Some careful positioning might be needed to minimize noise. Looks OK as-is.

This will work. Not paint-by-numbers, so an opportunity to learn and lean on the knowledge & creativity here.

Best .. Ian
Ian, thanks for your detailed answer.

I have read a few things here and there about the difference in the tubes.

Has anyone used other tubes in a Dumble clone? Would there be benefits? Differences in the sound?

Have you experienced it yourself? I have ever used an amp with KT77 one KT88.

Humbly.

Fred.

Fred, learning everyday!

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didit
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Re: HRM needs some Lovin'

Post by didit »

The KT series are quite similar in design & character to venerable 6L6, and 6550 too. Gather others regularly enlist some of them in Dumble designs --- Dumble even, as stories go. Personally not so Dumble familiar. Have a first, a ODS derived project, planned for the fall. Look forward to that. Past times used/abused KT77, KT88, 6550, 6CA7, 6L6WGC-STR (TAD) and some others. They all work well. Have differences one can hear. Purely personal taste --- current production preference is JJ KT77 (and some others) and EH 6CA7. Both behave without evidence of stress and have stable bottom end. KT77 has a clarity in the high-mid and above so long as I don't really overdrive. A significant difference is some of these have high filament current requirements, but 6.3V @ 6A won't have that problem.

You may find if those 6L6 that came with are the more rugged end of that specific type, so can please your ears at a sensible bias point so that fresh tubes are unnecessary.

Best .. Ian
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Re: RE: Re: HRM needs some Lovin'

Post by fred.violleau »

didit wrote:The KT series are quite similar in design & character to venerable 6L6, and 6550 too. Gather others regularly enlist some of them in Dumble designs --- Dumble even, as stories go. Personally not so Dumble familiar. Have a first, a ODS derived project, planned for the fall. Look forward to that. Past times used/abused KT77, KT88, 6550, 6CA7, 6L6WGC-STR (TAD) and some others. They all work well. Have differences one can hear. Purely personal taste --- current production preference is JJ KT77 (and some others) and EH 6CA7. Both behave without evidence of stress and have stable bottom end. KT77 has a clarity in the high-mid and above so long as I don't really overdrive. A significant difference is some of these have high filament current requirements, but 6.3V @ 6A won't have that problem.

You may find if those 6L6 that came with are the more rugged end of that specific type, so can please your ears at a sensible bias point so that fresh tubes are unnecessary.

Best .. Ian
From what I understand and have read these last few days, KT tubes seems a little more hi-fi then the 6L6. Am I wrong?

I am going through Morgan Jones' s book to try to understand a little more on tube amps. Will come back to the tube choice and trannies abilities when the chassis is taken care of ;)

Thanks for all the info Ian and looking forward to read on your own build!

Fred, learning everyday!

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

Post by fred.violleau »

M Fowler wrote:It's a little bit high secondary voltage but you could run 6550 or KT88 for something different then the old run of the mill Dumble clones.
Use a tube rectifier 5U4 or 5V4 to bring secondary down if you want. Also, reverse zener diode on HT center tap say a 50v zener to bring it down approximately 45v.

I like upright PT mounting leaves lots of extra room in the chassis for other goodies.
Thanks for the infos Mark! I thought at first that trannies in that position would produce hum. But the amp was quite quiet when iddle. Good To confirm the upright mounting.

I love doing things differently, specially if it may bring some originality in the sound of the amp.

I will resume this conversation as soon as I settle down the chassis (2 options underway) and will then probably dive deeper in the coupling of the trannies and the amplification unit of this build.

I feel priviledged to have you guys walking me trough all this.

Thank YOU.

Fred, learning everyday!


fred.violleau
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Re: HRM needs some Lovin'

Post by fred.violleau »

A little quickie for those of you who owns the archives of this great forum.
I am designing a new dumble clone chassis. In order to speed up the process I was wondering if someone could point me in the direction of some existing files.

I have crawled through the forum and have found different old threads, but none has a complete schematic of the chassis (or I have not found these yet) with all the holes and dimensions. If none exists then I will gladly contribute. Otherwise I would spare precious time as I will modify it anyhow to expose the HRM pots in the front and add the on/off HRM bypass as well.

Again thanks for your help.

Fred, learning everyday!


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