Build complete - 6G6B Bassman Redux

[ToneMerc]

I've started a 6G6B build, nothing fancy just the stock circuit with an upgraded adjustable bias supply with test points. Initially I was going to set it up with switchable rectifier types then I decided to skip the cool factor.

See updates


TM

[Roe]

looking good. keep us updated!

[LarryLarry]

Looks good dude! Just finished the wiring on my bastard bassman last night. I'm using a recycled Fender Sidekick Bass 35 ss chassis, a Weber PT and an OT from a Knight mono amp that ran 2x5881s (old but good Tung Sols). Currently running a GZ34 but will try the SS rectifier tonight and all my voltages are super close to the schematic. No hum, no idle noise at all with the volumes down

But...
I've got a lot of hiss on the Bass channel when I turn up the volume with no guitar plugged in. I omitted the .002 capacitor that runs to pin 6 of V2 to avoid too much bass on that channel. Could this be the cause? It's not there with the guitar plugged in, and the channel sounds great.

The Presence pot only seems to work in the last 20% of the sweep. I have the lead running through the 56k resistor going to the 4 ohm tap of the OT, which I think is correct.

[M Fowler]

That looks great.

[LarryLarry]

Just realized I have 68k resistors on each of the 2 channel inputs - but they are single inputs. I think I need to reduce them to 33k like the Rocket...

[ToneMerc]

Main board resistors mocked up for fitment.

TM

[CHIP]

TM,
Did you make the chassis?

[ToneMerc]

TM,
Did you make the chassis?

No, got them from Dario Gomez when he started selling off his remaining parts.

TM

[ToneMerc]

Power board wired

TM

[LarryLarry]

Are you doing the 1st 2 filter caps in parallel 6G6 style or in latter Bassman style series? I can't tell if you've got a wire underneth running from + to - on the 1st 2 caps. If they are in parallel, what are the 2 resistors (220k I presume) for?

I did mine in parallel. I have 470vdc B+ (in standby mode) and my caps are rated at 600vdc so I'm good.

[ToneMerc]

Are you doing the 1st 2 filter caps in parallel 6G6 style or in latter Bassman style series? I can't tell if you've got a wire underneth running from + to - on the 1st 2 caps. If they are in parallel, what are the 2 resistors (220k I presume) for?

I did mine in parallel. I have 470vdc B+ (in standby mode) and my caps are rated at 600vdc so I'm good.

Instead of two 20uf's in parallel, I used two 80uf's in series. Yes, there's a wire under the board. I didn't see any reason to build it without the balancer/bleeder resistors.

TM

[LarryLarry]

First let me say that I am an admitted novice here!

What is the advantage of series and the balancing resistors on the 1st stage of filtering vs parallel?

You only need the balancing resistors if they are in series, right?

My understanding is that as long as the B+ voltage in standby mode is well within the limits of the filter caps, there is no reason to put them in series. Back in the day, I don't think they used caps rated at 600vdc so I can understand why they did them in series.

[tubesinside]

Nice build.....like the turret idea.

[ToneMerc]

First let me say that I am an admitted novice here!

What is the advantage of series and the balancing resistors on the 1st stage of filtering...................?



My understanding is that as long as the B+ voltage in standby mode is well within the limits of the filter caps, there is no reason to put them in series. Back in the day, I don't think they used caps rated at 600vdc so I can understand why they did them in series.

1. Resistors will bleed off voltage, so there's some additional safety factor built in.

2. At one time there were 600V caps, my guess is that there wasn't a 40uf 600V available so they just paralleled two to get 40uf. However, by adding two in series the total voltage rating is increased for that node.

One day and my guess is inside of 10-15 years, commonly found axial 450-600V lytics will cease to exist. In 10 years if you need to recap that amp and fresh 500/600V caps axial lytics don't exist, what additional work will you have to do? If you wire that node in series, down the road 350-400V axial caps can be used with no additional rework.

TM

[LarryLarry]

Good info TM - thanks! I always appreciate when somene takes the time to explain this stuff to me!

In my case, the filter cap assembly will have to be pulled and dismantled whether the caps are in series or parallel. So if I have to change them, it won't make a difference time-wise. OTOH, if someone else has to change them - then after they pull the cap cover and get done cursing or laughing their arses off, they may just chuck the whole assembly! (I used perf board and a lightswitch cover).