'63 Blonde Bassman 6G6B

[Mark]

I had a repro tapped pot from ages ago and the taper of that pot was 10% which is a lot different from the original pots which were roughly 30% taper. I did give this feedback to the vendor who I bought the pot from and other sellers hoping the taper would be changed in the future. I don't know what the current production pots are like.

[Colossal]

this is one 200k Center Tap, NOS so the quality may be there even if the reference for that tap is center. I had purchased the replacement for the 350k/70k from antique electronics a few years back and I'm just getting to this project. That four-wide connector is an odd fit so I removed it and started searching for another replacement for a virgin build. That was how I came up with the 470K Pot which looks totally different and more like the one Fender used back then, Thanks for the update

Thanks for posting those photos, very cool to see them! I have thought of making a pot and even 3D printing a custom wafer from conductive carbon (if I could get a real NOS tapped pot to design from), but Martin's SPICE simulation is pretty darn close to the real deal, probably just fine for the application. Tony has milled the boards and I should have them soon. They are made from 1/16" black G10/FR4 board and I will sand them to a dull matte to pay homage to the Fender boards, but without the conductivity problems. I opted to add a few little changes here and there, such as a balance pot for the phase inverter, dual bias pots, and a couple of other indulgences. At Katopan's behest, I opted to go with a stock build.

[73GTV]

Do not purchase the pots I listed earlier from Ebay. The 200K Center tap is real or OK


Please review these photos of the 1Meg Pot.

I ordered these to check out the resistance point of that tap.

US Stock 2x 1M ohm 2W 6mm Round Shaft Rotary Taper Carbon Potentiometer WTH118
(Fake Item)
Note: it is an ear to the casing itself or Ground to case!!!

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[Colossal]

Rest assured, I won't be purchasing any pots from ebay

My design is locked in and only awaiting boards.

[JazzGuitarGimp]

A few years back, Weber were selling a modern-day equivalent of the 350K with 70K tap pots. Don’t know how close it is to the real thing, but I bought one to use in a ‘61 Fender Concert style build I am working on. The tone stack sounds great to these old ears...

Ciao,
Lou

Edited to add link: https://www.tedweber.com/wp354at

[katopan]

Note: it is an ear to the casing itself or Ground to case!!!

Wow! Too good to be true then. Thanks for letting us know.

[dorrisant]

Rest assured, I won't be purchasing any pots from ebay

My design is locked in and only awaiting boards.

They are on the way to you. Looks like delivery is today.

[Colossal]

Rest assured, I won't be purchasing any pots from ebay

My design is locked in and only awaiting boards.

They are on the way to you. Looks like delivery is today.

And boards received. They look great!

[dorrisant]

[Mark]

Picture of the boards?

[Colossal]

Picture of the boards?

I will post them later. I did some testing, sanding the black G10/FR4 board material to emulate the Fender boards. I used two very fine grits with alcohol, polishing to a matte finish. It took quite a bit of work to get the look I wanted. I should have them staked later this week.

EDIT: Here are the drilled boards

6G6B Boards.png

[Mark]

They look good.

[Colossal]

Well, here it is.

Bassman 6G6B Circuit.jpg

Bassman 6G6B Chassis.jpg

Bassman 6G6B Cab.png

Bassman Tube Chart.jpg

This was a "parts on hand" build; a bit of a mashup. First, a big thank you to Mark Fowler for the chassis and faceplates. Thank you, my friend. Thanks and appreciation also to Tony Dorris (dorrisant) for CNC milling my boards. I gave him the dxf files and he graciously milled them. I took some inspiration from Tonemerc's 6G6B build (https://ampgarage.com/forum/viewtopic.p ... 47#p226747) using (Kiwame) carbon films for plates and signal path and (Takman REY) metal films for cathodes and grid leaks, as I had these on hand from past builds. The amp is very quiet at idle, aside from the usual gain hiss. The power transformer is a Blonde Bassman clone with the primary wound for 117VAC, so I variaced down the mains to set the idle current. A while back, I had some little step down transformers with multiple primary and secondary taps wound and will dedicate one to the amp when I put it in a box. This is a stock 6G6B build with a few mods:

1) Dual bias pots, one for each 5881. This worked out quite well and current can be dialed in precisely to the desired value for each tube. I used an Apex matched set of Tung-Sol 5881s. The Fender 6G6B schematic shows -54VDC on the grids but at about 436VDC on the plates, this amounted to 17mA per tube. I warmed it up to about 50% dissipation at 26mA per tube or -50VDC on the grids.

2) Heaters elevated to DC. There is a divider and cap tapped off the bias tap giving +60VDC. I like to do this with amps that have cathode followers and pretty much any amp.

3) LED lamp in place of the #47 bayonet lamp. Again, another divider off the bias tap to supply a 3.2V warm white LED. It is biased to 15mA with a 330R. For fun I paralleled the divider with a 10nF ceramic and it makes the lamp fade perfectly when the amp is powered down. A bit of nostalgia for the old incandescent #47 lamps.

4) The SS rectifier diodes are also bypassed with 10nF ceramics, Dumble style. Again, had a bunch of these caps on hand, and, why not?

5) Bias test points on the back. I repurposed the Death Cap ground switch to switch between the 1R current sense resistors on the power tubes. Click it left and it's the left 5881, click it right and it's the right one. Works great and quite handy.

6) The OT has a 4R and 8R tap. NFB is taken off the 4R tap and wired to the extension speaker jack and 8R is wired to the main jack.

7) PI balance trim pot. I used a 10k trimmer between the 82k and 100k plate loads on the PI. It is set for 300V on the inverting side and 294V on the non-inverting side. You can definitely hear the effect. It sounds very fat and sustains like a bell. I think this is a very useful feature.

8 ) Martin Manning's Tapped Treble pot mod (1M1 & 75k across 500kA) on the Normal Channel. Sounds great. Nice sweep. See here: https://ampgarage.com/forum/viewtopic.p ... 43#p174243

9) Presence pot is wired Marshall style, 5kB pot and 100nF to ground off the wiper. Yes it scratches, but I don't care and it's much better than the 25kB -100nF parallel to 4k7 version, IMO.

I used wire nuts on the load and neutral connections for Phil S. Phil, I know how you love wire nuts Don't worry, the leads are soldered and held by both the wire clamp and strain relief. Tonally, so far, I am very happy with the sound. The Bass channel is unique and sounds great. Nice and full. I decided to just build the amp stock at Katopan's behest. Good call, Craig. The Normal channel sounds killer. I haven't had a chance to really open it up yet.

[pompeiisneaks]

Wow that looks beatiful!

If I'm seeing correctly I see a missed solder joint, the joint just to the right of the first blue sozo cap on the left side of the board, on the bottom end of the orange drop and the resistor in the 'V'. It does look like, though that may not be as it seems. I note it looks like you might solder from the bottom instead of the top as I noted a few others looked almost 'not soldered' but you could see some had flowed in from the other side and partially covered the hole etc.

Either way, outstanding looking amp!

Audio samples coming?

[Colossal]

Wow that looks beatiful!

If I'm seeing correctly I see a missed solder joint, the joint just to the right of the first blue sozo cap on the left side of the board, on the bottom end of the orange drop and the resistor in the 'V'. It does look like, though that may not be as it seems. I note it looks like you might solder from the bottom instead of the top as I noted a few others looked almost 'not soldered' but you could see some had flowed in from the other side and partially covered the hole etc.

Either way, outstanding looking amp!

Audio samples coming?

Thanks man! That joint is actually fine. It's a trick of the light and probably some left over flux filling in the space, giving it a dark, empty appearance. I solder from the top. I won't be able to get to a sound sample soon, well, maybe with a phone, but I recently sold my interface and need to get another.