Ampeg R12-R Reverberocket variant

[Sonny ReVerb]

Making some progress on my Ampeg based 6V6 amp. It's basically an R12-R with an early brownface tone stack. I worked up a schematic and board layout. I already populated the board. I'm waiting on a faceplate and a chassis punch to enlarge some holes for the octal pre-amp tubes. See what you think.

[Sonny ReVerb]

Board and chassis

[Sonny ReVerb]

Heaters

[Sonny ReVerb]

Done. I missed a solder joint on the 1k power resistor, but caught it on testing. Cab build next.

[Sonny ReVerb]

More pics

[shooter]

but caught it on testing

that's always the best way for find issues, sometimes we get in a hurry to "plug in" an play, then get all bummed n bent when it don't play

nice build

[Sonny ReVerb]

Thank you, Sir.

[Sonny ReVerb]

This amp is pretty clean even at max volume. Definitely not the garage rock amp that Ken described, but I did change the tone stack. Maybe it adds more load than the original. Nice chewy cleans, though. I used a bunch of NOS tubes I had - the 6V6s are a mismatched 6V6GT/6V6GTA pair. I've ordered some new JJ and Tung Sol 6V6s to see how they compare.

Can you treat the reverb recovery (V2-B) like a normal gain stage? I was thinking of adding a switchable bypass cap for a gain boost.

[sluckey]

Can you treat the reverb recovery (V2-B) like a normal gain stage? I was thinking of adding a switchable bypass cap for a gain boost.

That won't work for this circuit because the dry signal is inputted to the cathode of V2B. If you put a bypass cap on V2B cathode you will kill the dry signal. Then all you'll have left is the boing boing from the reverb circuit.

[Sonny ReVerb]

I'm really enjoying this amp. Nice cleans and the reverb is excellent.  Cab thread: http://el34world.com/Forum/index.php?topic=22350.0

However, there is an odd noise riding on some notes. It seems to be somewhat frequency dependent. I tried swapping tubes, re-flowing solder joints/grounds, and chopsticking. No luck yet. You can hear the noise on the repeated notes at the end of the clip.

https://soundcloud.com/user-208278224/vw-noise-track-1

 I've heard these octal preamp tubes (6SL7,6SN7) tend to be microphonic. Could that cause this type of noise?

[Sonny ReVerb]

No suggestions, eh?

I finally had a chance to pull the chassis out of the cab and do some more testing. I'm an amateur with a scope, but I looked at the signal at several points. When I had the scope connected to the input the volume control affected the signal, but not in amplitude. When the volume control is off the scope shows noise(?). Increasing the volume slightly causes the trace to clean up. Increasing the volume more causes the noise to reappear until the control is at max. then the clean signal reappears.

https://vimeo.com/245077942

Next I connected the scope to pin 2 of V2 - the plate of the triode section after the volume control. The signal was clean with a corresponding change of amplitude with a change in the volume control.

https://vimeo.com/245078360

Any ideas? Why would the volume control show a change to the signal at the input?

[shooter]

your input signal might be to small for your scope to "display clean", try scoping the input signal NOT connected to the amp n see if it looks the same.

having the vol interact with the input signal sorta tells me there might be a ground issue
Ghost notes are a B ch to nail down.  you probably won't find it with a single tone/frequency.

where does it show the most, on the fat strings or the skinny ones?

[silverfox]

I have heard ghost notes can be attributed to the power supply. Are the 20uf reserve caps sufficient?

silverfox.

[Sonny ReVerb]

Thanks, guys.

your input signal might be to small for your scope to "display clean", try scoping the input signal NOT connected to the amp n see if it looks the same.

I believe the function generator level is set to 150mV, but I'll scope it directly to see what it looks like.

where does it show the most, on the fat strings or the skinny ones?

The sweet spot seems to be the sixth fret of the B string (F) for some reason, though it's evident on other notes too.

I have heard ghost notes can be attributed to the power supply. Are the 20uf reserve caps sufficient?

Actually, the first filter cap is 40uF, which is a bit stout for a 5Y3 rectifier. Most 5Y3 datasheets show 20uF-32uF max for the first filter cap. I wonder if that could be causing the issue?

[pompeiisneaks]

The filter cap being over rated for the rectifier isn't a problem for sound, it means the rectifier may die prematurely.  It puts stress on it.  You shouldn't over do that, no, try putting a 32 on it and see if it changes it, though. 

[Sonny ReVerb]

I did some research on the first filter cap issue before I installed it. The consensus seemed to be that NOS 5Y3's should be fine, as long as there is no arcing within the tube. Electrolytics have wide tolerances, so you never really know what you have in there anyway.

On the noise issue, after much troubleshooting I believe it is caused by V2 tube rattle. I tried another tube in that position and it was making the same noise, but when I grab the tube the noise stops (don't try this at home kids, the tube could be hot). These octal dual triodes (6SN7/6SL7) tend to be microphonic. I'm going to try some o-ring tube dampers and call it a day.

[octal]

Are you still wanting more gain out of this? If you reduce the value of R15, you will let more "dry" signal through. V2A has 100% dry signal going though it, and is cathode coupled through R15 to V2B to mix the dry signal in with the wet signal coming back from the reverb tank.