New build: Sluckey VK22 /with Bieworm mods :)

[pieterfx]

Hi all,
want to show of this build.
MASSIVE thanks to Sluckey for the Vibro King based design. And MASSIVE thanks to Bieworm for pioneering this design and making some cool changes (mostly 6v6 and bias wiggle trem), ánd for sharing all those changes and ideas on this forum. There is a topic about this here: https://el34world.com/Forum/index.php?topic=31722.0, but I didnt want to hijack that thread. But all credit to them.

I followed Bieworm in making this 6V6 with NFB and bias wiggle trem. I put the NFB as a switch in the back, the FAT switch as a switch in front. Single input in front. I kept the mid pot.

I built a similar amp before this with 6g15 reverb circuit in front of a single channel AB763 (topic here https://el34world.com/Forum/index.php?topic=31575).

I had a lot less trouble getting the Vibro King running.. everything worked exactly as is should from the first power up! And it might be the honeymoon phased but I LOVE this amp. Did hours of rehearsal at high volume yesterday and it held up 100%. Compared to the AB763 breakup is easier to dial in a bit earlier using the mid control. Less bright, but can be bright. And with all the reverb and drip from the 6g15 circuit. And with the best trem ever.  Everything someone playing in a surf/punk rock band would ever dream of.

One question: only remaining space to mount a reverb tank in the headshell is upside down on the ceiling. That would require a tank with last letter A (open side up) in the code... anyone know where to buy one of those in Europe?

Faceplates and logos are in the works.

[RoadShow]

One question: only remaining space to mount a reverb tank in the headshell is upside down on the ceiling. That would require a tank with last letter A (open side up) in the code... anyone know where to buy one of those in Europe?

Faceplates and logos are in the works.

Here's the one I ordered from Antique Electronic Supply: P-RMOD-9AB3C1B
I mounted it open side down as specified with spacers, but made a .040 aluminum cover that I inserted within the flexible grommets to close off the bottom.

They do sell some open side up ones with other spring counts, lengths, and delays:
https://www.amplifiedparts.com/products/reverb_tanks?filters=2663a2689c260a2663

[pieterfx]

Thanks for this. I now also found a European shop (Banzai in Germany) where I ordered the "open side up" version of the reverb tank. Great!

One other question: doing some experiments and measurements, according to https://robrobinette.com/Tube_Bias_Calculator.htm the 6K6 is now biased at 40-45%. Which is very low, as I understand for cathode bias it could go to 100% with no problem?

Am I right in thinking that more power output from the 6K6 would drive the reverb tank (even) harder?

If yes, what is the easiest/best way to do this? get more plate voltage is my thinking? So maybe just connect the 6K6 plate to an earlier B+ node? Or do I change the cathode resistor.
(I get this question probalby exposes that i have some underdeveloped basic understanding of tubes..)

[RoadShow]

Am I right in thinking that more power output from the 6K6 would drive the reverb tank (even) harder?

If yes, what is the easiest/best way to do this? get more plate voltage is my thinking? So maybe just connect the 6K6 plate to an earlier B+ node? Or do I change the cathode resistor.
(I get this question probalby exposes that i have some underdeveloped basic understanding of tubes..)

https://el34world.com/Forum/index.php?topic=31722.msg350749#msg350749

[pieterfx]

Back with another post on this amp. I'm really loving this amp its gorgeous.

I have been tinkering with the 6K6 tube to get the most drip out of it. Besides trying different reverb pans, I have lowered the cathode resistor from 1K to 330 Ohms. This is the original value used in Sluckeys VK-22 design. I also lowered the B+ dropping resistor from 4,7K to 2,7K Ohms. This got me 240V on the 6K6 plate and 11V on the cathode. According to Rob Robs bias calc, this gets met 90% plate dissipation. Noticeable stronger driven reverb, so yippy!

> As the reverb circuit is basically a champ single ended circuit, I can bias at this high level, correct?

BUT. The 2,7K Ohm 5 watt dropping resistor gets REALLY hot. Its dropping 110V. So is passing 40mA's. Which makes sense because that's 35mA's from the 6k6 plus a bunch of 12AX7's. So that's 4,5 Watts on the resistor, correct? Very close to the max 5 Watt..

> Do I have this right? Or am I missing something why this resistor gets hot? Is the solution just a bigger resistor?


UPDATE: added the schematic. also added original Sluckey's VK-22

> one more question: it seems Sluckey connects the 6k6 plate to the B node, where Bieworm's mods connect to the C node... why? Is one or the other preferred?

[SEL49]

BUT. The 2,7K Ohm 5 watt dropping resistor gets REALLY hot. Its dropping 110V. So is passing 40mA's. Which makes sense because that's 35mA's from the 6k6 plus a bunch of 12AX7's. So that's 4,5 Watts on the resistor, correct? Very close to the max 5 Watt..

Good safety rule of thumb...

Measure/calculate the actual power dissipated by a resistor. Double that number. Use the next higher common wattage.

In your case the resistor is actually dissipating 4.5W. Double that to 9W. Actually use a 10W resistor.

[Willabe]

I have been tinkering with the 6K6 tube to get the most drip out of it. Besides trying different reverb pans, I have lowered the cathode resistor from 1K to 330 Ohms. This is the original value used in Sluckeys VK-22 design. I also lowered the B+ dropping resistor from 4,7K to 2,7K Ohms. This got me 240V on the 6K6 plate and 11V on the cathode. According to Rob Robs bias calc, this gets met 90% plate dissipation. Noticeable stronger driven reverb, so yippy!

> As the reverb circuit is basically a champ single ended circuit, I can bias at this high level, correct?

BUT. The 2,7K Ohm 5 watt dropping resistor gets REALLY hot. Its dropping 110V. So is passing 40mA's. Which makes sense because that's 35mA's from the 6k6 plus a bunch of 12AX7's. So that's 4,5 Watts on the resistor, correct? Very close to the max 5 Watt..

> Do I have this right? Or am I missing something why this resistor gets hot? Is the solution just a bigger resistor?

Please post the schematic, not the layout drawing.

[pieterfx]

Added schematics (and a question) to the post from yesterday, thanks.

[Bieworm]

> one more question: it seems Sluckey connects the 6k6 plate to the B node, where Bieworm's mods connect to the C node... why? Is one or the other preferred?

I think I used the C node out of convenience or to get some lower voltage to the plate of the 6K6. I can’t remember the exact reason.
Congrats on the build by the way.
 

[pieterfx]

Thanks!

I experimented with where I connected the 6K6 to the B+. In the end I kept it in the same place, but switched the cathode resister back to 1K. This got me 70-something% dissipation. No audible difference in the sound of the reverb, but a big difference in the power and heat through the 5W dropping resistor. So Im going to keep it there.

Alsmost done with the head and faceplates, will post pictures when fully done!

[Bieworm]

This is my private version. I built it in an old Gretsch cab in the original chassis. That was a real challenge… ship in a bottle stuff

[pieterfx]

To close of the topic I wanted to share the final picture of the head with faceplate and logo. My designs were laser etched and printed by a friend. I think its cool looking :)

On to the next build...

[Willabe]

Amp looks great!

Is that the real light blue tolex that Mojo sells? I like it!

 

[pieterfx]

It’s baby blue tolex from banzai music in Germany. Great store.

[pieterfx]

Small update:
I have recorded with this amp, posted about it here https://el34world.com/Forum/index.php?topic=32879.0

Im building another one and I think more people should :). Im making a new/complete DIYLC file for this schematic (with the 6v6 and bias wiggel trem), will post that here when back from vacation.

[Bieworm]

Build a 3x10 combo for the full experience. It’s part of the Vibro King tone
I have a real VK but it doesn’t nearly sound as good as my 6V6 Goliath, which is my take on the Sluckey SVK22