'63 Blonde Bassman 6G6B

[Colossal]

I received a very generous gift of a chassis, doghouse, and octal cover from a forum member and buddy, and so I am building a 6G6B. This will be the 1963 transitional model with smooth blonde tolex, wheat sparkle grill cloth, black strap handle, Brownface front, Blackface rear face plate, and cream knobs. I have a pair of Tungsol 5881s and some TD 6L6-STR short bottles to try.

I plan to wire the Normal Channel per the schematic with Martin Manning's 350k tapped pot alternative. For the Bass Channel, I am thinking of taking Roe's suggestion of going with a K50 preamp. Power supply caps will be 2x80uF F&Ts in series with 220k balancing resistors for 40uF 600V and the rest 22uF, solid state rectified.

Questions for general comment:

1) Thinking about adding a trimmer for the PI. It is interesting to note the rather large difference between inverting and non-inverting plate voltages (+20V). Perhaps this is part of the Bassman magic and should remain left alone, or maybe it could benefit from some Dumblizing?

2) The Presence circuit is 4k7 || 0.1uF-25k pot. Was thinking about going with the older Marshall 5k pot and 0.1uF as the sweep is much more effective.

3) Chassis has a hole for a second bias pot. Might be useful to be able to be able fine tune each power tube and especially in conjunction with a PI trimmer. Again, not looking to add complexity unnecessarily but it could be useful.

Starting to assemble this weekend

Cheers, guys.

[sluckey]

I plan to wire the Normal Channel per the schematic with Martin Manning's 350k tapped pot alternative.

Hoffman sells an Alpha replacement if that interests you. Less than a penny per kilohm.

https://hoffmanamps.com/MyStore/perlsho ... =!ORDERID!

[Colossal]

I plan to wire the Normal Channel per the schematic with Martin Manning's 350k tapped pot alternative.

Hoffman sells an Alpha replacement if that interests you. Less than a penny per kilohm.

https://hoffmanamps.com/MyStore/perlsho ... =!ORDERID!

Hi Steve,

I thought I read something that said those reissue pots did not sweep like the originals, but that could be internet hearsay mixed with my pending senility.

[sluckey]

That would not surprise me. But it does sweep from 0 to 350K and it has a 70K tap. You could just redact the numbers on the chassis.

[katopan]

I had a real '64 transistion era (Blonde circuit, cream knobs but black tolex) in my hands a few years back and it inspired me to build my own. Fantastic amps!

You should reconsider installing a real tapped pot. It's part of the 6G6-B magic that the alternative circuit is lacking. I really like how it transitions from Blackface in the top end to treble roll-off Tweed in the bottom end. The Blonde has some great tones in the transistion area because of this that can't be found on the later Blackface era models. I actually built the stock schematic Bass channel and love it too. It's got a wide range of tone control and a thicker sound than the Normal channel. Great for guitar and actually fantastic for blues harp as well (totally different settings, but it can do both unlike most amps that have to be modified for harp). The Bass channel will also do jazz (I've used it when I filled in for a big band) but with the treble up it overdrives harder than the Normal channel with a different tone.

[martin manning]

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

[Roe]

I had a real '64 transistion era (Blonde circuit, cream knobs but black tolex) in my hands a few years back and it inspired me to build my own. Fantastic amps!

You should reconsider installing a real tapped pot. It's part of the 6G6-B magic that the alternative circuit is lacking. I really like how it transitions from Blackface in the top end to treble roll-off Tweed in the bottom end. The Blonde has some great tones in the transistion area because of this that can't be found on the later Blackface era models. I actually built the stock schematic Bass channel and love it too. It's got a wide range of tone control and a thicker sound than the Normal channel. Great for guitar and actually fantastic for blues harp as well (totally different settings, but it can do both unlike most amps that have to be modified for harp). The Bass channel will also do jazz (I've used it when I filled in for a big band) but with the treble up it overdrives harder than the Normal channel with a different tone.

thanks - this makes sense. I've tried it but didn't care for it personally

[norburybrook]

what is this mysterious 'Tapped' treble pot you speake of?

Funnily enough I've one chassis left in my lockup and I was looking at this exact amp as a possible last build for me hence I arrived here.

Would it give me something my Tweed deluxe , princeton or silver face Bandmaster reverb wont give me, or do i have it all covered with those? I like the idea of two independent channels though with the possibility of a a higher gain channel and a standard fender ish one switchable with a simple AB switch or ABY for both.

Are they both in phase? I presume so as they have the same gain stages.


M

[martin manning]

The tapped pot is now a relic of the early '60's. It has a fourth terminal which is connected to the element at a fixed location, about 1/4 of the way up from the bottom. See the Fender 6G6-B schematic, normal channel, for a schematic representation.

That might be a different sound for you, definitely not like a Tweed Deluxe, but closer to the Bandmaster. Brian Setzer puts it to good use, along with a Space Echo, so you can get a good idea of what it can do for his music. Rig discussion here https://www.youtube.com/watch?v=0HU84CCvST8 (12:37 for the amp discussion). You do have two channels to work with if you build the whole thing, so you can voice them differently to get some variety. Most people reconfigure the bass channel. Member Tonemerc did a few of them; I saved notes somewhere on his bass channel mods.

[Colossal]

Last week, I was able to get the transformers in, pots, switches, faceplates on, and start wiring infrastructure. All ground points are in. I still need to finish the board drawings. I hope to do that this week, get them cut and drilled, and ready for staking. As ToneMerc did with his build, I added bias taps and repurposed the Ground switch to select between power tubes. Also, I utilized the extension speaker jack for an 8R tap as I'm using a Bassman OT with 4 and 8R taps. I am still leaning towards a K50 preamp in place of the stock Bass channel. Normal channel will remain stock except for Martin's tapped pot mod. Also adding a second bias pot (there is a hole) and will add a PI pot trimmer I think, as there a large DC difference between inverting and non-inverting sides with that 6k8 tail.

Marcus, for me, the inspiration of this amp is the great cleans. Very punchy and articulate but warm and full. I have read a lot of mixed views on the Bass channel in its stock form. There is the infamous wiring error on the bass pot with some amps which can make for a thin sound with guitar. There are four stages and set up almost verbatim for a Trainwreck preamp anyway. I will likely up the PI entrance cap from 500p to 1000p and maybe change the output section to 0.047uF. I don't want to go too far off the beaten path though. The Bass channel could also be set up as a Rocket preamp. Decisions...

[martin manning]

Are they both in phase? I presume so as they have the same gain stages.

Unfortunately they are not. The second stage on the bass channel is a CF.

[norburybrook]

Are they both in phase? I presume so as they have the same gain stages.

Unfortunately they are not. The second stage on the bass channel is a CF.

ah.. that would only be an issue then if you wanted to use both, switching would not be an issue.

and this tapped pot?... what's that all about?
edit: google sorted that out.

M

[Mark]

I have a 6G7a Bandmaster and I have the 350K pots. The taper is different on the pots. The originals have a 30% taper whereas from memory the reissue pots have a 10% taper. The bass pot has a 10% taper.

The amp is sitting on the bench at the moment if you have any questions.

[katopan]

Hi Martin. I thought I had seen your alternative circuit, but thanks for attaching it because I actually hadn't.

I added it to the LTSpice simulation file I used for the Blackface vs 6G6-B treble sweeps I posted. Here is the result. Please check the schematic and make sure I've read your layout modification correctly. Has the same basic transition from standard TMB treble to Tweed like roll off. Also looks like it suits 10% taper which is good for the pots we can get these days. But the shape is different, where the mid scoop looks more pronounced and the treble content higher.

When I found out the postage cost of getting a couple sent here, and before I found out there was someone on the AGGH forum that had a stock of them locally here in Oz and would've been happy to sell me one, I made one. Don't recommend it but it gave me an authentic tapped pot with the right resistances and proper 30% taper.
https://sites.google.com/site/chosenaud ... /tappedpot

Sorry for the sidetrack Dave. I have a soft spot for the 6G6-B so look forward to seeing your build come together.

[Colossal]

No problem at all! All relevant sidetracks welcome. And thanks for posting the SPICE simulation of the tapped pot!