Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frank57 on November 22, 2012, 03:22:39 pm

Title: Reeves custom 6 schematic so far how wrong?
Post by: frank57 on November 22, 2012, 03:22:39 pm

I found a clone layout of this amp that's no longer in production and tried to draw up a schematic.
It's close but not sure if it's 100% bang on.
The tone stack and preamp are the same as the custom 12.
Does it look right so far? I got stumped on the el84.

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: drgonzonm on November 26, 2012, 06:00:40 pm

I don't see your output transformer and how you plan to wire the output side. 

Also, does the reeves show a cap in parallel with a no-load wire, and then in series with a resistor?  I would guess, and it is a huge guess, that the resistor off the cathode of the pentode is wired parallel with a capacitor. 

Also, a couple of SE amps I've seen, have the plates from the 12ax7 feeding the screens on the pentode, you have high voltage feeding one of the screens on the pentode

If you look at champ aa764, it takes the approach you are taking regarding the feeding a pentode from the p/t.  Other than component selection, resistors and caps, there are only a few ways of wiring a dual triode, pentode SE amp.

Gibson provided a dual output tube valve SE amp, the clavioline.  I guessing that Gibson also made a similar amp with a single pentode.

Good luck. 

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: frank57 on November 28, 2012, 05:56:53 pm

Here's some shots of real reeves amp.
Maybe you can see better what he's up to in the real amps.
The custom 6 and the nice sounding custom 12.
Did I get the preamp part right in my schematic?

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: jazbo8 on December 03, 2012, 09:59:58 am

There are some mistakes in the schematic. I re-did it in JSchem: https://dl.dropbox.com/u/1326040/Reeves%20Custom%206%20Clone.jsch (https://dl.dropbox.com/u/1326040/Reeves%20Custom%206%20Clone.jsch)

Does anyone know the specs for the PT and OPT?

Jaz

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: drgonzonm on December 06, 2012, 05:37:14 pm

Frank57, could you post the numbers on the transformers.  Maybe we can sort out the specs from cross-referencing the xformers.

Thanks in advance.

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: frank57 on December 17, 2012, 02:36:22 pm

I know the transformers were Heyboer for sure.
The Reeves custom 12 has Heyboer as well.
I think you can see the numbers in this shot.

They might be custom made though.
Reeves Custom 12 has the exact same preamp with 2 56 or 68k resistors on the high and low input
but I don't know where the 1meg resistor is.The only difference is the power section with 2 el84.
Parralel single ended?

Both are Class a amps.
Cool schematic that Jazbo8 did!
I transformed it into a jpg and added a note about the input.
There's some variation in the reeves 6 with this shot showing some bigger caps.

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: jazbo8 on December 17, 2012, 03:15:06 pm

Quote from: frank57 on December 17, 2012, 02:36:22 pm

I know the transformers were Heyboer for sure.
The Reeves custom 12 has Heyboer as well.
I think you can see the numbers in this shot.

Can't make out the numbers, the picture is a bit fuzzy...

They might be custom made though.
Reeves Custom 12 has the exact same preamp with 2 56 or 68k resistors on the high and low input
but I don't know where the 1meg resistor is.
One 5.6k and one 68k, I think, but the way is drawn on the schematic will work just fine.

The only difference is the power section with 2 el84.
Parralel single ended?
Yes two EL84 in parallel.

So are you going to clone one? Seems like a pretty straight forward project.

Jaz

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: frank57 on December 18, 2012, 01:26:35 pm

I'm thinking about it but I've never built an amp from scratch.
I've worked on the amps I have and pedals and so on.
It doesn't look that difficult which would be good for me.
I would rather try the custom 12
but maybe the Custom 6 would be cheaper and easier.
What kind of transformers can be used with it?

What exactly did he do in the power section on the Custom 12?

That I can't see clearly in the photos.

I think the Custom 12 transformers are
OT 3500 SE HTS-7904
PT-250 HTS 0323 or 8323

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: jazbo8 on December 18, 2012, 02:45:19 pm

Since you have not done a scratch build before, you may want to consider starting with a kit, because it is pretty easy to make mistakes in ordering parts (not to mention time-consuming unless you already have many of them on hand). And Hoffman offers some kits to choose from.

As for the Custom 12, it is just one more tube+socket and of course larger transformers to handle the extra power. What speaker are the amps mated with?

Jaz

Title: Re: Reeves custom 6 schematic so far how wrong?
Post by: frank57 on December 28, 2012, 03:23:30 pm

A small correction.
Reeves definitely uses 250 pf cap.
You can see it in the photo of the reeves custom 12 way in the corner.
What does the 22k resistor on the bass pot do?