New Project: 6U8/6V6 amp

[duhvoodooman***]

Comin' along nicely there, Tung! :

I gotta tell ya Tung, I am totally in awe; : : : ; of what you and DVM do with your skills in making amps, pedals, etc.

Don't be so impressed, Pie. If Tung and I can handle this stuff, how hard can it be??

[tunghaichuan***]

Comin' along nicely there, Tung! :

Don't be so impressed, Pie. If Tung and I can handle this stuff, how hard can it be??

Yeah, really. :

I gotta tell ya Tung, I am totally in awe; : : : ; of what you and DVM do with your skills in making amps, pedals, etc.

OMG, I would be ready for the loony bin for sure.

Thanks for the kind words, Python.

Update:

I spent the afternoon attaching the flying leads and installing the board. I spent quite a bit of time soldering down the leads from the transformer as they can be a real PITA to deal with.

Here are a couple more pix:

Flying leads attached to board

Board installed in chassis

I've got quite a bit more wiring done than shown in the above picture. More pix to follow.

tung

[duhvoodooman***]

Man, you are flyin' along on this one, Tung! :

[F_BSurfer]

looking good.......what kind of transformers you using on this one

[Ch0jin]

Nice work as usual Tung

I'm especially interested in what you think of the VVR in practice. I might have a lot of spare time in the near future, and I'm thinking of rebuilding my old frankenstein amp to sort out a few niggling issues. As it's probably going to remain around 50W (don't want to change trannies etc) being able to dial down the voltage and subsequent volume is appealing.

I'm also waiting eagerly to hear about the compression control

[tunghaichuan***]

Nice work as usual Tung

I'm especially interested in what you think of the VVR in practice. I might have a lot of spare time in the near future, and I'm thinking of rebuilding my old frankenstein amp to sort out a few niggling issues. As it's probably going to remain around 50W (don't want to change trannies etc) being able to dial down the voltage and subsequent volume is appealing.

I'm also waiting eagerly to hear about the compression control

The VVR is the last circuit I'm going to put in. I still need to order some of those NTE mosfets, which are pricey. The VVR shown previously only works with cathode bias amps. There is another VVR circuit for push pull amps which automatically tracks the bias voltage.

The compression control is merely a pot to regulate the screen. Randall Smith has a patent on it, so I would never be able to use it in a production amp

I'm attaching the preamp schematic I'm working from so that you can check it out yourself.

tung

[Jipes***]

That's fascinating Tung I'm really curious to her and see the final result I have a friend who loves to play around with Tube amp but you seems to be kind of a "Tube Guru" isn't it

I have unfortunately two left hands (I'm right handed) so I will never ever give it a try on this type of construction but I'm really curious and admirative for your work :

[tunghaichuan***]

looking good.......what kind of transformers you using on this one

Thanks!

The power transformer is a vintage Triad R6A. I've used it for several tweed Princeton builds, and it works great. The output transformer is a Fender Champ 12 unit. 5K:8 ohms, rated at 10 watts. It should match well with the JJ 6V6S.

tung

[just strum]

Comin' along nicely there, Tung! :


Don't be so impressed, Pie. If Tung and I can handle this stuff, how hard can it be??

You and tung are too modest. Through my eyes, you two are artist.

To put it in perspective:

After doing a simple mod, you two are to me as:

My golf game is to Tiger Woods (play one round with me and you will realize how big of a compliment that is).

My guitar playing is to Buddy Guy, Clapton, SRV, Townsend....

[tot_Ou_tard]

Fantastic tung!

Is there any way we can get clips?

Vood, when are you gonna build an amph?

[duhvoodooman***]

Vood, when are you gonna build an amph?

You must mean, "when are you going to build another amph":

http://www.thefret.net/showthread.php?t=5702

Answer: I dunno. Won't be real soon, since I have the new Egnater to play with for a while, at least. But I still want to do a "proper" amp build some time--something in the 15 - 20W range probably. A Marshall 18W clone or a Fender 5E3, most likely, but who knows? These recent projects of Tung's look REALLY interesting, so maybe one of those. Choices, choices, choices....

[tunghaichuan***]

Update:

I had a chance to play my amp last night for a while. Mrs. Tung was out so I could crank it without annoying her.

I tested it with a bunch of pedals, a Weber Mini Mass and my Hohner and Warmoth guitars. The Hohner has true single coils, but I don't know any of the specs on them. The Warmoth has stacked humbuckers, SD Hot Stack Strat pups which are very bright for humbuckers.

Observations:

1. The amp is dark. Even with the Tweed Princeton tone control all the way up, it is not very bright, even with single coils.

2. The tube I have in there is microphonic and while the IERC tube shield helps, the amp still squeels a bit with all the controls dimed. Probably needs some shielded wire to the grids. I've only tried a 6U8 tube in the amp. I need to try some 6GH8 and 6BL8 tubes.

3. The amp does not like pedals as well as I thought. I tried a BBE Green Screamer (TS808 clone) a Washburn Soloist OD, a Rocktron Blackjack booster/distortion and my BYOC Triboost. Most of these sound very good through my Little Giant and Valve Junior heads. They only sounded so-so with the 6U8 amp.

4. The natural, cranked OD sounds pretty good, but the tone control has to be turned up all the way to keep the bass notes from farting out. The Triboost sounded the best on the germanium setting, with treble boost sounding the best and mid booste a close second. The amp did not like the full range boost settings on the pedal. I also tried the amp through a Weber Mini Mass. This is the older style without the bright settings. With this amp the MM could really use them.

I need to get the compressor circuit sorted out first. Then I may try reducing the coupling caps a la Vox to get a brighter, chimier tone out of the amp.

I'm going to try to get some sound samples up in the next few days so you can hear what the amp sounds like now.

Stay tuned...

tung

[BigDaddy]

I am about to start on a similar build. It's a 6V6 SE power section with a 6U8a preamp tube. I do not know exactly how to approach this. Do I use the triode as the first stage then TS then pentode into the 6V6 or the pentode first. Or should I add another stage from another pentode or triode before or after?

So I was wondering if you have sorted out the amp and have a schematic to share.

I was thinking of possibly using a 6AT6/6AV6 then into the 6U8a. Maybe using the triode part to drive a CF TS into the pentode.

[tunghaichuan***]

I am about to start on a similar build. It's a 6V6 SE power section with a 6U8a preamp tube. I do not know exactly how to approach this. Do I use the triode as the first stage then TS then pentode into the 6V6 or the pentode first. Or should I add another stage from another pentode or triode before or after?

So I was wondering if you have sorted out the amp and have a schematic to share.

I was thinking of possibly using a 6AT6/6AV6 then into the 6U8a. Maybe using the triode part to drive a CF TS into the pentode.

I built the amp using Kerry's schematic from the AX84.com site. Post or PM your email and I'll send it to you.

I used the pentode section as the input gain stage. The triode was used as the driver for the 6V6.

You could reverse that though, use the triode as the input gain stage and pentode section to drive the 6V6.

The 6AT6/6AV6 will give lots of gain cascaded into the 6U8. Be prepared to use a voltage divider circuit to pad down the gain.

tung