4x 6v6 Donor amp head - Any conversion suggestions

[Trenchard_UK]

Hi all

I have a 4 x 6v6 reverb two channel hand wired head that I would like conversion suggestions for.

It is a beautifully crafted piece, built by a highly respected UK builder (now retired) and tweaked/modified by him for me a few years ago.  Now that I am retired myself, and have built a couple of Kit amps, I am looking to see if it is possible for me to modify it myself using my learned experience to give it (and me) a different life !  I would have to work from a layout though because my brain cannot cope with a Schematic alone.

I would like to re-use as many components as I can - salvaging from the removed eyelet boards where possible and keeping the 40w PT, OT, and Choke(s) and Rectifier valve in place.  That should keep me busy through the winter months.

If anyone has any suggestions, please let me know.

Thanks

[dogburn]

I'd say it would help if say what kind of amp you would like to have. Something loud, something quiet? Clean or overdriven? Fender, Marshall, Vox, Supro, or what sort of sound? How many preamp tubes are already installed?

If it were me, I'd probably go for a Pro Reverb because I don't have an amp in that power range.

[tubenit]

It would be helpful for us in helping you to know the entire tube lineup, please.  Also, is there something about your amp that you don't care for?  Is there an amp design out there that you particularly like? 


With respect, Tubenit

[kagliostro]

If you have a schematic of your amp to share it will help to see what it is feasible

Franco

[66Strat]

Maybe a four 6V6 Deluxe Reverb variant?

[Trenchard_UK]

Hi all, to answer your questions, Perhaps a brownface sound? Here is a gut shot of the doner amp.  I have printed schematic and transformer data, but not sure if I am allowed to upload them.  Would not wish to upset anyone.

[passaloutre]

Holy Jesus that’s a lot of knobs.

Brownface, lots o tubes…I’d go for one of the brown Fenders with the harmonic tremolo. Concert or Super, just use your four 6V6 instead of the two 6L6.

[kagliostro]

Obviously can't know how it sounds but it is a very cool construction with good components

In some way it seems not a so good idea to gut it, may be some mod .....

EDIT: May be your amp is a clone of Dumble ODS HRM with reverb, modded in the Power Section to have 6V6 tubes ?

Franco

[Trenchard_UK]

Channel 1 is Blackfaceish and Channel 2 is a Boogieish type of overdrive. I don't want to gut it entirely, I would like to leave the power section in situ, along with the rectifier valve and reverb- assuming that I can find a layout for a new pre-amp board that will give me reverb.

When I had the mods done a few years ago, it changed the amp somewhat and it did not work for me anymore.

EDIT:  How would my PT and OT transformers stand up to running 2x6L6 instead of 4x 6V6 valves/tubes.  Here is the data.

[dogburn]

Seems like what would be best if for you to tweak the circuit here and there, maybe restore the Blackface channel to what it was (and maybe tweak some) and change the other channel to more Brownface configuration. You might also change some preamp tubes to other versions.

The people who could really help you here would probably really need the schematic to give you specific direction.

[glass54]

At the risk of being damned, there is very little new (under the sun) so sharing the schematic should not be a problem 
Leos original designs have been copies by everyone, Randall went crazy with OD, Jimmy copied almost exactly and HAD refined preamp and ultra-stiffed the power supply.
So I would encourage you to be a nice guy and share the schematic 😊
We’re all nice people here.
Regards
Mirek

[kagliostro]

Dogburn  preceded me and said exactly what I think

Franco

[Trenchard_UK]

Here is the Schematic.

I can follow some of it, but it does not make easy sense to me at my level of experience.   Relating it to the layout is impossible for me, that is why I don't think that I could modify it, and opted to replace the pre-amp board with something else that would use the existing PT, OT ,Chokes, 4x6v6, rectifier, reverb - and if not 6v6 then perhaps run 2x 6L6 - working from a layout.

[kagliostro]

OK, do you remember which are the mod you asked to be inserted ?

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Don't worry before, if someone identify how to mod the circuit It will be easy to you to find the component in the real circuit and ask to confirm the identification, then proceed to the mod

Franco

[Trenchard_UK]

When I received the amp head, it had a two button footswitch.  One to change the channel and the other to switch the reverb on and off.

Because I was playing in places where there were bright lights or dark stage areas, I asked the builder if he could:

- change it to a three button footswitch with bright different coloured LEDs on it.

Button 1 when activated to provide a volume boost to the clean channel for clean solo playing. LED when on.
Button 2 when activated to change the channel for OD.  LED when on.
Button 3 when activated to provide a volume boost to the OD for solo playing. LED when on.

The amp came back with a 3 button LED footswitch that now had a din plug on the end instead of a jack plug- no problem it plugged into a replaced DIN socket and functioned exactly as I had asked for.

However, I did not give any consideration to the 30 ish watt overall output of the amp and potential loss of volume before asking for changes.  When I tried the changes, it made the un-boosted clean channel too quiet to use effectively, and when boosted via the footswitch the volume came back up a bit but sounded very different losing any BF type of sparkle.  Much darker.

The amp did have a pull "FAT" pot but the pull no longer worked after the changes so I expect that got incorporated into the boost somehow.

The channel change worked out ok, again it was lower in volume but the boost bought the volume back with a bit more gain.

I guess my options are to - find a way to return it to the original state- but it was never really loved so I would also like to change the second channel a bit or cut my losses and rebuild it into something else using salvaged parts where possible. Maybe an early bluesy kind of Dumble type with reverb or Brownface amp.

I would like to keep the rectifier if possible (for the sag).  I am at heart, a blues player.

Regards

[kagliostro]

Channel 1 is Blackfaceish and Channel 2 is a Boogieish type of overdrive

So attention must be concentered in the differences between this two circuit and what is in your amp (to try to restore it)

BTW, your 3 footswitch seems to ignore the activation of the reverb, in wich way do you active it ?

At the moment the PPpotentiometer what do if pulled & pushed ?

EDIT: Your channel 1 remember a lot the AB763 Vibrato Channel, may be you can start from there to restore the channel






Franco

[Trenchard_UK]

Reverb is always on.  It can't be turned off but it can be turned down

Pushing or Pulling the pot does nothing, but the sweep operates normally to adjust the gain for the lead channel.  If you look at the pot in the gutshot picture (5th from the inputs) you can see witness marks where something had been removed from the lower lugs.

Here is the front face to provide context to the gutshot.  I did have a black and white picture of the pre-changes provided by the builder - will try to find it.

[kagliostro]

I've just added something to my previous post

----

I did have a black and white picture of the pre-changes provided by the builder - will try to find it

This will be really hepfull


Franco

[Trenchard_UK]

This picture was with the amp on delivery from the builder.  That was in November 2016, so this is pre-changes.

[kagliostro]

Unfortunately it is a low resolution image and is not of great help ....

However the most useful thing is the schematic

I'm not so skilled but on the forum there are members that can give you the right councils

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One thing you can do is to send to the builder a copy of the schematic and ask if he can put on it indication on the components that are mod respect the original or ask for an original schematic before the mod were applied

Franco

[Trenchard_UK]

Yes the image is not the best.

You have been a great help, thank you.  I am sure that in time I will resolve it with your and other people's help.


Regards

[kagliostro]

As Channel 1 Is similari to the AB763 Vibrato Channel may be It will help you to read the explanation on this link

https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm

Franco