'63 Blonde Bassman 6G6B

[katopan]

Good to hear you're progressing with the build.

I've got to do a simple demo clip one day of the Bass channel. Everyone passes it by but it is great for guitar. It has more gain on tap (still mild) with the treble turned up a bit than the Normal channel. The clean is different but sounds fantastically smooth. Treble up it's still very bright, treble down is killer for jazz.

[Mark]

You can get more gain out of the amp using a Tweed PI stage. If you are after more gain from the whole amp.

http://ampwares.com/schematics/bassman_6G6-B.pdf

https://ampgarage.com/forum/viewtopic.p ... G6B#p88816

There are a few threads on different mods on Bassman 6G6 here.

https://ampgarage.com/forum/viewtopic.p ... 6B#p327315

[Roe]

the gain of the PIs seem virtually identical: https://www.ampbooks.com/mobile/amplifi ... alculator/

[Mark]

Are you sure that is correct?

A Tweed or Marshall amp needs more gain from the PI than a Brown or Black face amp. The cathode resistor on the Tweed circuit is 470 ohms versus 820 ohms in the Brown face circuit.

[Colossal]

Hello Katopan,

I recall there being some issue over the schematic of the Bass channel and specifically over how the tone stack was wired. Some owners said their bass channel was thin for guitar, others say it was usable. I believe this had to do with how the bass control was wired (or not wired).

My interest in the amp was largely in how good the amp sounds through the Normal channel for clean tones but also fully dimed into a load. I could probably be happy not even building in the channel, but that is worse than leaving a triode unused! I thought the Komet preamp a logical replacement. I am not much of a high gain player these days though. I am far more interested in the clean to mean aspect and maximizing touch sensitivity and all that, design wise.

[katopan]

Hello Katopan,

I recall there being some issue over the schematic of the Bass channel and specifically over how the tone stack was wired. Some owners said their bass channel was thin for guitar, others say it was usable. I believe this had to do with how the bass control was wired (or not wired).

My interest in the amp was largely in how good the amp sounds through the Normal channel for clean tones but also fully dimed into a load. I could probably be happy not even building in the channel, but that is worse than leaving a triode unused! I thought the Komet preamp a logical replacement. I am not much of a high gain player these days though. I am far more interested in the clean to mean aspect and maximizing touch sensitivity and all that, design wise.

There was certainly an issue with the way some of them were wired. I built to this schematic & layout and it's the good version (matches your repost earlier in the thread).
http://ampwares.com/schematics/bassman_6G6-B.pdf

The original I borrowed before building my own was modified with a 220k in place of the 1M in the Bass tonestack slope resistor. It also had a Bass side mixing resistor as 1M instead of 470k to change the relative volume between channels. I built mine stock with the idea of modifying it if I didn't like it, but left it be as I think it sounds great. Oh, and it had a 12AT7 in the PI socket. Made it surprisingly Blackface in gain level and tone. Replacing that with the 'proper' 12AX7 restored back the missing part of the Blonde character.

Fully dimed volume, treble and presence is fun! Not Wreck or Marshall fun, but does this snappy overdriven thing that stereotypically sounds great with a Tele or Strat. Either channel, they just sound a bit different to each other and the stock Bass channel overdrives the power stage a bit more with everything up full compared to the Normal channel. Clean to mean is there like many other amps, but not like in the way of a Wreck or even a Marshall 18 Watt. Touch sensitivity isn't like those two other amps either. In my mind that's due to the PI and power stage, so a different preamp isn't going to change that.

Anyway, depends on how you are building as to whether it's easy to build the stock Bass channel and then replace it with something else later, or if you are better now deciding on a permanent circuit to your liking for that channel.

[katopan]

Just out of interest because I've already got it, here's the sweep response of the full Bass channel from LTSpice modelling. If you put the bass tonestack into Duncan TS Calc you'll see it's almost a ramp increase toward the treble end. Even after the treble control stage it's actually very treble heavy. It's actually the final stage 2nF plate cap that equalises everything back to something more normal. But the range of sweep is huge and goes from quite treble heavy to fairly bass heavy.

First is the full Bass channel response. Second without the last stage plate cap. Third the Duncan TS of just the upfront bass stage tonestack. Sweeps are just 0%, 50% & 100% of both treble and bass controls.

[Colossal]

Thanks for posting those sweeps!

[Hotwatt]

Tapped pot - https://www.tedweber.com/wp354at

You probably made it past this hurdle by now and Martins home grown pot tapping method looks good but just thought I'd post this.

[Colossal]

Tapped pot - https://www.tedweber.com/wp354at

You probably made it past this hurdle by now and Martins home grown pot tapping method looks good but just thought I'd post this.

Hi Hotwatt,

Thanks for posting that link. I have heard mixed reviews on the reissue tapped pots as not having the same sweep as the originals. As such, I will be trying Martin's home grown pot, as I have heard it is excellent (I saw what you did there).

I"m glad you bumped this thread. I am a little behind on the build but will post more progress soon. I have the chassis hardware in, switches wired, pots and jacks in, jacks wired and coax runs down, power section and AC wired. Need to get back to my boards.

[Hotwatt]

Cool Colossal. I was on the fence about what to build earlier this month as the amp build bug had bit me again. I was almost going to build a 6G6B but decided to do a 6G16 VV instead. My dad had a Blonde Bassman in the 80's it was a beauty not sure which revision it was. I'm bought 2 of those tapped pots for my 6G16, they do seem somewhat overseas-ish. I'll find out how they sound, hopefully by summer.

[73GTV]

Katopan, have you tried simulating this tapped pot alternative I came up with? I think it comes pretty close to the original.

After reading this post several times, I wondered if you could use this from eBay a 470k Potentiometer with the tap, higher resistance than the called for 350K/70k Tap, but it is from China, etc, so might take a bit of time to arrive.
470K Ohm Variable Resistor Single Turn Rotary Carbon Film Potentiometer
eBay item number:
233174171632

https://www.ebay.com/itm/WH118-1K-470K- ... 0005.m1851

Also, there are: US Stock 2x 1M ohm 2W 6mm Round Shaft Rotary Taper Carbon Potentiometer WTH118
eBay item number:
371900394522
Seller assumes all responsibility for this listing.

This is a 1 Meg Potentiometer pair, stocked here in the US if you can drop the resistance, this should also work, worth a try in my book.

[Colossal]

Hello 73GTV,

Thanks for your comments. Picking back up on this thread, I tabled this project for a while due to Covid and other pressing projects.

As for the tapped pot, the chassis is already wired for Martin's tapped pot substitute. The difference in response is small enough. I have it on good authority that the currently available reproduction tapped pots do not respond adequately.

A while back, I decided to change my board layouts a bit, adding a few small features here and there, and worked with Dorrisant who kindly milled a set for me on his CNC. I will be posting update photos shortly as the amp will be finished pretty soon.

[73GTV]

Hello 73GTV,

Thanks for your comments. Picking back up on this thread, I tabled this project for a while due to Covid and other pressing projects.

As for the tapped pot, the chassis is already wired for Martin's tapped pot substitute. The difference in response is small enough. I have it on good authority that the currently available reproduction tapped pots do not respond adequately.

A while back, I decided to change my board layouts a bit, adding a few small features here and there, and worked with Dorrisant who kindly milled a set for me on his CNC. I will be posting update photos shortly as the amp will be finished pretty soon.

Great, Yes, I read that post on the modification of that pot; I can't wait to see how that one goes.




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.

eBay item number:
324238103726
Seller assumes all responsibility for this listing.

I

[katopan]

I have it on good authority that the currently available reproduction tapped pots do not respond adequately.

We've had another 6G6-B based build (single channel) on the Wattkins forum by someone else and the 10% taper on the new ones was reported by that builder to be a bit of an issue, supporting what we've heard before.