6v6 Wreck Build...Finished w/ clip

[studiodunn]

I'm going to build myself a little grab and go 1x12 and decided to try a 6v6 Wreck build. I have a donor amp with a viable PT, but I will need a OT. I will probably go with a Classic tone. Though I'm not sure yet if it will be an express flavor or a 20w fender flavor. That said, I'm sure values will need adjusted once the OT is ordered. As usual, I have been reading up and have armed myself with just enough information to make me less dumb. Slowly but surely this whole circuit thing is coming into focus.

Most of the layout is taken right from the Kelly schematic, but I wanted to use the 2nd half of V2 as a boost. Did I implement the Push Pull pot right?

6v6Wreck01.png

TWXprsSchem.pdf

[Paulg]

Very cool! I’d be interested in seeing an updated schematic when you’ve fine tuned it.

[beezerboy]

any forward motion on this project? looks interesting

[mwelch55]

I have used this transformer from Antique Electronics for two 20 watt builds. Output Transformer primary impedance is 6.6K and has 8 and 16 ohm taps. Primary impedance is the same as a trainwreck transformer. Both of the amps built with this transformer have high gain Marshall preamps and sound incredible. They are both cathode biased, but thinking of converting one to switchable cathode bias/fixed bias. I can switch between 6V6 and 5881 without re-biasing.

Mike

[studiodunn]

Updates coming soon. I have just started on the board and will get pics up once I populate.

[studiodunn]

Finally got things soldered up. On to the chassis. i managed to cram it all on one 11" board, but I will surely be cussing myself if I need to pull a part

Also Note: on the layout above the final two rectifier diodes and the bias caps are shown backwards.

Wreck_pop01.jpg

[studiodunn]

Well, I got the amp together and fired up with no smoke, it sounds fizzy and under powered.
I've checked all values and continuity and found nothing offensive. The amps noise floor is great and poking around with a chopstick revealed no iffy connections. I suspect this blocking distortion as the amp has an audible lag after striking a chord and muting the guitar. It takes a 1/4 second for the signal to build back up.

.....So eyes still needed

Voltages seem within reason?
Bias @ -31
392 @B+1
388 @B+2
344 @B+3
309 @B+4
281 @B+5

Classictone - 40-18065
Hammond 1620 OT

UPDATE:
Bias resistor went from 220 to 200 to get me -32v
I got the voltages right on by changing out the the 18.2k resistor for a 40k
Volume was low due to the infamous 470R PI resistor...I had a 470K in its place. The volume instantly came up, but the blocking distortion was still there.
I found that I had put a .047 Cap on the presence pot instead of a .1u, This was causing allot of squealing, so fixing this helped.
At this point I have the amp sounding pretty good by removing the V1-3 bypass cap and adding a 470k grid leak resistor.
I also removed the bright cap all together and like it much better.
I'm thinking about adding a voltage divider at the last stage to try and get a little more grind from the amp.

IMG_5883.jpg

IMG_5881.jpg

IMG_5880.jpg

IMG_5885.jpg

IMG_5884.jpg

[gingertube]

1K5 is insufficient gridstop for 6V6. You need more like 5K (4K7) minimum. The lower gm tubes like 6V6, 5881, 6L6 etc. need higher value gridstops than high gm tubes like EL84,EL34, 6CA7, KT88 do. 1K5 is OK for this latter lot but not for the first lot.
Having said that, for the purposes of reducing blocking, I would normally run 33K or even 47K gridstops on the 6V6.
I would also "routinely" use 10K gridstops on every 12AX7 triode.
On the EL34 Express I built, I found that V1A and V3A and B needed gridstops to cure paasitic oscillation, so just put 10K on all of them.

[studiodunn]

1K5 is insufficient gridstop for 6V6. You need more like 5K (4K7) minimum. The lower gm tubes like 6V6, 5881, 6L6 etc. need higher value gridstops than high gm tubes like EL84,EL34, 6CA7, KT88 do. 1K5 is OK for this latter lot but not for the first lot.
Having said that, for the purposes of reducing blocking, I would normally run 33K or even 47K gridstops on the 6V6.
I would also "routinely" use 10K gridstops on every 12AX7 triode.
On the EL34 Express I built, I found that V1A and V3A and B needed gridstops to cure paasitic oscillation, so just put 10K on all of them.

Yep. After much reading I went ahead and put 33k grid stoppers on the 6v6s and things got
Much better. I found some issues with wiring that were causing lots of problems. The lesson on this build is centered around OT placement. Having it down by the V1 obviously creates some challenges and on an express build it seems even more so. It took about 3 different wiring layouts before everything stopped sounding like a theremin. After sorting the wiring and going back over the voltages I ended up going back to 18.2k on the B+ and the voltages were really close to the TW Schematic. I also went ahead and put the bypass cap on V1.

Amp sounds really good, but I’m still tweaking. I will get a clip up once I get ready to box it.

[studiodunn]

Here is a rough iPhone clip of the amp. I still have a bit of blocking distortion that I need to find. I have Grid stoppers on every triode and still haven't gotten rid of all of it.

Where this thread started and where this amp ended up are pretty far apart, but all in all I'm happy with the end result.

[Colossal]

Well done! I especially like the howlin' dog on the faceplate. Very nice!

How big are the grid resistors on your output tubes?

[martin manning]

I agree, sounds good! I don’t hear blocking distortion, though it does get a little buzzy at times. I like the faceplate too... a “little wolf” ;^)

[studiodunn]

Well done! I especially like the howlin' dog on the faceplate. Very nice!

How big are the grid resistors on your output tubes?

Thank you. The OT's have 10k resistors on them.

I agree, sounds good! I don’t hear blocking distortion, though it does get a little buzzy at times. I like the faceplate too... a “little wolf” ;^)

Thank you Martin. Maybe I'm hearing something that isn't there, I am a rookie after all. There just seems to be little sizzle/buzz/something extra that sounds off from the core sound.

I had to reroute the presence and TS wires to the top because crossing the OT primary wires was causing allot of grief.

IMG_6607.jpg

[norburybrook]

I think that sounds great nice clean, nice crunch and nice wreck style OD.

Love the dog too. I think in a 1x12 grab and go combo it will be lovely.




M