The other Webster 6L6 amp

[bmccowan]

Hello,
I wanted to follow-up on a project. When 1Blueheron started that Webster Allen Organ amp that Sluckey helped him with, I had the near identical amp and was going to follow along, but convert mine to a pentode preamp. A major health crisis hit the family and I was out of commission for a bit. But I just went back to finish it and fired it up a few minutes ago. I went pentode 6SJ7 for V1, loosely following some Valco and Gibson schematics from 40s - 50s. As with BH's amp, I kept the 6SL7 PI and the power tube setup unchanged. All new caps. Amp sounds great. I redid a Gibson BR-6 a few years ago and this sounds similar but with that distinctive 6L6 sound instead of the 6V6s in the Gibson.
BH, I am glad your amp turned out well, and I'm sorry I had to disappear. And Sluckey you were a trooper! Those drawings you did helped me too, despite the fact that I was going pentode; so thanks again. And I think I'll try that raw control. I have not drawn a schematic, but could do so if anyone is interested.
Mac

[sluckey]

I'd like to see your schematic and some pics of the amp too if you got the time. I bet others would too.

[bmccowan]

Sure - will do. I still (allegedly) work so I may be slow. I just started to learn JSchem prior to having to step away from amp stuff. I find it somewhat awkward to use, but will go back to it.

[1blueheron]

Mac,

Sorry about the family health issue but that's great news on the amp.  Glad it turned out so well.  I will be revisiting mine shortly.  I still need to get a good cabinet built for it.  The airline project got me sidetracked a bit.

[bmccowan]

Thanks blueheron. Unfortunately Cancer seems to be hitting a lot of families these days. And ha! I know what you mean about sidetracked projects - I have many! The Airline project is cool. It does not look like a Valco product, did you determine if it was a Dano or an Electrolab by chance?
I should have photos and maybe a schematic of the Webster up later today. I'm very impressed with Websters' components and build quality.

[1blueheron]

Yes, the Airline is definitely a Danelectro product.  Hoping the rest of my parts show up tonite or tomorrow so I can test the rig out.

Been fooling with the Baldwin breakdown/salvage in the meanwhile.  Lots of nice iron and tubes but the chassis layout sucks for a conversion.  Will be doing a scratch build from parts on this one I believe.

Cancer is no fun.  Most of my family has died from cancer of one form or another.  Lost my uncle to it this past week.   

Eager to see pics of your Webster.

[bmccowan]

Sorry about your Uncle. Uncles are the best - just don't ask my nieces and nephews.
Dano should be fun - I have one in the wings - a 1953 Special. Very cool but a real basket case.
Going to try and upload my schematic and photos now.

[bmccowan]

If this works - a schematic and a couple of photos are attached. I'm just learning JSchem, but I think I did ok - might be mistakes, let me know please.
Things I will do - some kind of simple tone control - maybe a presence control. I like to keep these old circuit amps simple though. Its how they sound best in my opinion. And maybe I'll make a face plate, and maybe a VVR.
Things I should do - plug the empty holes. Move the ground for the large filter cap to a PT bolt, although its actually quiet as I have it.
And I might change the power tube cathode resistor and switch to 6V6s as I have a bunch of really nice JANs.
See later post for corrected schematic

[bmccowan]

So in thinking about tone controls, I considered that the amp has a lot of negative feedback. I disconnected it and the amp was too noisy. So I upped the feedback resister from 16K to 56K and added a 5K pot with a 0.1 cap to ground - similar to many tweed fenders. Nice change. More grit, but amp still quiet. If I leave it this way, I will update the schematic. Truth is the 5K pot does not have much of an effect, so changing the resistor value is 95% of it.
I still do not have a conventional tone control, and may or may not add one. Would appreciate any thoughts on possible tone controls.

[Ed_Chambley]

So in thinking about tone controls, I considered that the amp has a lot of negative feedback. I disconnected it and the amp was too noisy. So I upped the feedback resister from 16K to 56K and added a 5K pot with a 0.1 cap to ground - similar to many tweed fenders. Nice change. More grit, but amp still quiet. If I leave it this way, I will update the schematic. Truth is the 5K pot does not have much of an effect, so changing the resistor value is 95% of it.
I still do not have a conventional tone control, and may or may not add one. Would appreciate any thoughts on possible tone controls.

With the pentode I would probably use cap switching as a tone control, but the Dr Z, Route 66 is a EF86 to a Bass and Trebel stack and I like it a lot.

[bmccowan]

That Z-R66 setup is a good idea. I built a 6V6 version of that amp a couple years back. I think I used that stock tone circuit. I also built a Z-28ish with a 5879 and that amp sounds great. I should revisit that schematic too.

[bmccowan]

Hello again - updated schematics attached. Removed to correct a mistake
Changes to amp - increased the neg feedback resistor from 16k to 100k and added a presence control. The amp now has the right amount of grit for playing at home which is all I do these days.
Changes to the schematic - fixed two resistor position and value errors on the preamp. Upped the size of some of the eye test text. And annotated a bit.
Cheers

[PRR]

Did Gibson really tie the 2Meg G2 resistor to plate instead of to B+?

That will work, but we usually take Rg2 to B+.

[sluckey]

I think he probably meant to draw it like this...

     https://el34world.com/charts/Schematics/files/Gibson/Gibson_br6f.pdf

But Gibson did some crazy stuff too, like this...

     https://el34world.com/charts/Schematics/files/Gibson/Gibson_br4.pdf

[bmccowan]

Hi,
Sluckey is right. I meant to draw it, and did wire it, similar to the BR-6F, which is one of the amps I looked at to figure how I wanted to configure this one. Thanks for pointing it out - I have not done many schematics. Will fix.
BTW - I am new to JSchem. Do you know of any good tutorials, as I am have some issues. Such as, components jumping around when I try to increase the label font, the undo command does not work, etc.

[bmccowan]

Corrected (I think) schematic. It's great to have folks like PRR and Sluckey on this forum helping us out!

[PRR]

> Gibson did some crazy

Actually, triode-wiring a 6(S)J7 was VERY commonly done. I believe the 6J7 came first as a high gain tube, but triode-wired it is sweet low-hiss triode. 6J7 was made in large quantity at low price. As the selected 1620 it was THE small tube in tons of broadcast gear. Although there is a 6J5 which sometimes IS a 6SJ7 internally, the 6J7 and its no-cap kin 6SJ7 were ubiquitous into the 1950s.