Other Amps

I’m rebuilding my 6g15 reissue…

126

Heres another thought.In the original schem there is no 1.5k grid stopper between the wiper of the dwell pot and the grid of the 12AT7 it feeds.Do you have one there?If not try putting one there.If you do have one there,it needs to be connected directly to the pin of the tube socket,not on the board.You need to clip one lead as short as possible and solder that lead directly to the pin,so the body of the resistor is almost touching the pin lug.

127

I could try that. Still, I wonder why it all works correctly with one tube and not another.

128

I just spoke with Gerald Weber and he seems to think it is just a bad AT7.He agreed that if it was a circuit problem,the AX7 would make it worse.I thought that earlier,but you did say you tried 3 different AT7's.A problem like this doesnt necessarily mean the tube is totally shot,it could just have a problem that manifests itself in certain circuits.Try the grid stopper and if that doesnt work,I'll go thru my tubes and find an AT7 that works in my unit and I will send it to you.In the meantime using the AX7 is fine.Some people like using one in that part of the circuit.Having more gain there will make the reverb signal a bit stronger.

129

Yes. I have three AT7s here, two JJs and an old Sator. All yield the same results.

130

If you try the grid stopper I recommended,it might be just enough to shun whatever is causing that buzz.If you look at a schem for the re-issue,they have one there.Dont know why they added it to the re-issue,but maybe you found the reason.

131

A Surf Fragment...

That's a recording I made tonight. Wanted to make a sample of my re-built reverb unit in semi high-fidelity.

It was a good excuse to dust off the microphone and mic-pre. Big improvement over the built in imac mic of course.

That's my '06 6118-LTV...

– JBennett

A Surf Fragment...

That's a recording I made tonight. Wanted to make a sample of my re-built reverb unit in semi high-fidelity.

It was a good excuse to dust off the microphone and mic-pre. Big improvement over the built in imac mic of course.

That's my '06 6118-LTV...

– JBennett

BUENO

133

Okay. I've found one error I made in my circuit. Maybe someone can tell me if it could possibly be the culprit for my Dwell issues.

Under the doghouse, between two of the electrolytic caps I placed a 1K-2W resistor. The schematic calls for a 10K-1W resistor. Other than some rounded up/down capacitors on the main board this is the only discrepancy that I've found in my circuit and it's off by ten fold.

I thought this was just a bleeder resistor though so I don't see how this would make a difference, and I have looked at tons of photos of vintage units that used several values in that spot under the doghouse.

(yes, that's a Brown/Black/Red/Silver resistor, 1K, not a 10K which would be Orange instead of Red.)

134

It would send too much voltage to that particular tube.If it is feeding the 12AT7 it could possibly be causing the problem.It is a "dropping resistor",it drops the voltage from one point to the next,I would change it.It could very well cause a parasitic which could be the problem.

135

Just took a look at the schem.There should be a 1k 2w on the cathode of the 6K6 tube.Did you put the 10k there by mistake?The 10k would indeed be feeding the 12AT7 tube so if you did switch those two,you know what to do.

136

No. I put a 1K-2W resistor in both spots even though the resistor between the two electrolytics should be a 10K-1W resistor.

Otherwise it follows very closely to the schematic. All the resistors are exact, and some filter caps are approx.

137

Well,change that 1k to the 10k that should be there.Caps can be close enough,but that 1k/10k is a big difference and I'm guessing it is the problem.

138

Just ordered a 10K. Should get here within the week. I'll let you know how it goes.

139

Im betting you got to the bottom of this.Let us know when you get it.

140

So... I took out the chassis again, swapped in a 1w-10K resistor between the electrolytics.

Dropped in a 12AT7 tube and powered it up.

The buzz was GONE, and then it swelled up again, and then disappeared... so now it was intermittent. I noticed that as I put pressure on the dwell knob the buzz would fade out or fade in.

So, I loosened up the dwell pot and wrapped some buss wire under the pot and wrenched it back down figuring it might have been poor contact with the pot. That it could be the grounding of the dwell pot. Sure enough that did it.

I think the reason I ruled that out earlier was I jumped (with a 2 foot cable the pot to the chassis and still had the buzz and maybe it was interference that I was getting on that long jumper? I don't know.

Anyway, now I've got a 12AT7 in there, the correct resistor so now the circuit is just like a vintage unit, with the exception of the PT and full wave rectifier.

It sounds great (I like it better with the 12AT7) and thanks again to everyone for chiming in. I'm glad to have the last of the bugs worked out.

JB

Here are those improved solder joints on the brass... 60w iron to the rescue. image

The final guts: image

image

and the new 1w-10K resistor under the doghouse: image

image

141

Cool,glad you got it sorted out.

142

What did that cost you to convert? How much time did you spend?

143

I think I spent about 100 dollars on components/wires, and another 40 bucks on tools (wire snips/60w soldering iron/eyelet tool)

Time spent.... much more reading and researching the project than actual build time. The part that took the longest was the drilling of the chassis, and mostly because I decided to go with the big AC outlet.

The actual time spent at the table, soldering/assembling was probably under 6 hours total, and this was my first time doing anything like this. If I did it again I could probably do it in half that. I was VERY slow and second guessed everything I did.

Doing the wires that come off the main circuit board and go on the back of the board was the hardest part I guess, but as you get the hang of dealing with the wires it all speeds up.

I have a new baby kicking around the house so I had to squeeze the project in here and there 30 minutes at a time. Hence the long build thread. If I had an uninterrupted day, and had already understood the entire project from A to Z I would think you could easily do this conversion in a day, certainly in a weekend. It's a great intro project for tube amps.

144

This job can be done in a couple of hours,but J took his time,was careful and came out with a super neat,clean job and it works fine.Considering it was your first build of any kind,it was pretty much trouble free at the end,the problem you had was really minor,you done good.

145

Thanks Stokes.

yeah, keep in mind, I made my rebuild overly complicated by trying to stick right on the original layout. The doghouse added a bunch of steps that could have been avoided, as did the aux. outlet.

146

Probly best you stuck with the original layout,it is,afterall,a proven design,saved yourself a lot of time in the longrun having to chase down problems that may arise if you tried to redesign.I wouldnt describe those steps as being "overcomplicated".You were going for as close to the original design and did a good job of it.Now,on to your next build.Try a Tweed Champ,very basic and is the base to pretty much all amp circuits.Want something a little more complex,a Tweed Deluxe is a good start.

147

I can't build another amp yet. Not until I have space to keep it!

I do have the bug to buy one of those DIY ribbon mic kits. That, I could store and use.

148

Know what you mean about not having room.Since my boys have moved out,my wife wants to find a smaller home.I got 11 amps in my basement,half dozen guitars and my workbench for guitar/amp repair.A sizable woodshop in the garage.Thank god the boys took 2 or 3 amps each and a couple guitars,but a smaller place is out of the question,she aint happy,but I aint partin with my shit!


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