Single Tube Reverb

mcrracer · Post by **mcrracer** » Wed Sep 30, 2009 5:12 am

glasman wrote:
Bob-I wrote:I haven't had a chance to listen to your clip yet, but I switched my reverb to the one tube in Norm's layout. Sounds far better than the Fender reverb I had, but the biggest improvement was that the amp itself sounds better. It appears that there's less affect on the amps tone.

At first I felt that it was a bit weak so I paralleled 2 tubes to add depth. As it turns out there's plenty without this so I'll be putting it back soon.
A lot of the difference is the size of the mix resistor. In this application, smaller is better. BTW, the R10 on the schematic below should be 2W from 27K to 47K.

[img:761:337]http://www.glaswerks.com/schematics/reverbcir.jpg[/img]

Gary

Is T2 the spring reverb tank?

heisthl · Post by **heisthl** » Wed Sep 30, 2009 5:17 am

talbany wrote:It's actually 1/2 pentode and 1/2 triode...70% gain on the triode side like an AT7..

Specs..

Well then show us how you would use this tube to drive a tank and then recover the signal and mix it back in to the amp

talbany · Post by **talbany** » Wed Sep 30, 2009 5:43 am

Here is one way!!..You could mix it back at the PI if you like.what I did..Is this better than a 12At and 12 AX no!!! but I think it's better than a single AX...More drive from the pentode..Took me a while to dig it up..

Tony VVT

heisthl · Post by **heisthl** » Wed Sep 30, 2009 5:56 am

I've seen that schematic - Tony - I was just teasing you because you led me to believe you were going to drive with the triode side with your "70% gain on the triode side like an AT7" comment and I hadn't seen that yet.

talbany · Post by **talbany** » Wed Sep 30, 2009 6:07 am

Henry
That's cool!!! you gotta keep people honest around here...I'll have to start reading your posts a little more carefully now!!..LOL!!
We started implementing the 6bm8 in the Tomo F amp single ended and remember my partner tweaked it a bit.. When I get to the shop Ill open it up and see what we changed and get back on the final resting values...See ya SGT Red Plate...

Tony

mcrracer · Post by **mcrracer** » Thu Oct 01, 2009 3:59 pm

One more question what suggested value for the dropping resistor for B+5 (V5)? Thanks for the schematic,it explains what you were talking about .

glasman · Post by **glasman** » Thu Oct 01, 2009 5:27 pm

Interesting. I tried the 6BM8 several years ago as a reverb driver / recovery. It was ok, but for what I was doing, not much better than two sections of a 12AX7, this was back in my BD (before dumblitis) days.

I have also experiment using 12BZ7's Mucho more gain and current capability, but microphonic as a church bell

.

These days I prefer side-chained current driven reverb.

Gary

talbany · Post by **talbany** » Thu Oct 01, 2009 5:33 pm

Interesting. I tried the 6BM8 several years ago as a reverb driver / recovery. It was ok, but for what I was doing, not much better than two sections of a 12AX7, this was back in my BD (before dumblitis) days.

I have also experiment using 12BZ7's Mucho more gain and current capability, but microphonic as a church bell Smile.

These days I prefer side-chained current driven reverb.

I wanted to like the single 12AX and put it in several OD amps and we tried everything to get it to sound good..Don't get me wrong it wasn't horrible and as long as you kept it down low just enough to achieve the added dimension it worked fine...If you wanted to get more from it it got to a point where it sounded nasal..We just didn't think one side of an AX drove the tank hard enough in that particular design...Too each is own I guess...

If your using Fender iron what I used.. you can tap off after the PI supply...w4.7K or 2.2k..depending on where you land in the PI.. then filter at least 20 uf..You should shoot for around 280 on recovery side Hope this helps

Tony[/img]

glasman · Post by **glasman** » Thu Oct 01, 2009 6:05 pm

Actually I found putting a .1uf at the junction of the dropping resistor to ground gave me the best reverb level on my old SOD's. I tried E-caps at that location and found a poly was all that was necessary to force that point to AC ground.

But that was then.....

mcrracer · Post by **mcrracer** » Thu Oct 01, 2009 9:20 pm

Thanks Talbany

talbany · Post by **talbany** » Thu Oct 01, 2009 9:50 pm

Gary

Also try wiring the pentode as a triode.Bm8. Tie 6 and 7 together..I think might work better for you..

glasman · Post by **glasman** » Thu Oct 01, 2009 10:22 pm

It worked find, but that work was done 8 years ago. I am off on other missions these days and probably won't revisit the 6BM8 at this point in time.

Gary

markusw · Post by **markusw** » Fri Oct 02, 2009 7:56 am

talbany wrote:We just didn't think one side of an AX drove the tank hard enough in that particular design...Too each is own I guess...

Did you try a 12dw7 instead of the 12ax7? JJ makes them.
The 12au7 half might work better as a driver....

j-po · Post by **j-po** » Fri Oct 02, 2009 9:43 am

markusw wrote: Did you try a 12dw7 instead of the 12ax7? JJ makes them.
The 12au7 half might work better as a driver....

That's a tempting idea. The return stage would also have higher gain than any tube in the ecl family.

Aurora · Post by **Aurora** » Fri Oct 02, 2009 2:11 pm

How would one connect this in a Rocket??
feeding via a resistor directly to the main PI input, or through the lower cap that is grounded in the normal schematic?

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