Where can I find a 5B4 super chassis?

[olgoat]

My first 5e3 build went pretty well in no small part to lots of help from this forum.  I would like to build a 5B4 circuit for inclusion into a modified V-Front cabinet that is almost finished.

This is the circuit with 6 octal tubes, preamp amp section is 3 6SC7s with a pair of 6L6s and a 5U4G rectifier.

Any idea where I can purchase a nice looking chassis to use for this project?

Thanks for any thoughts and tips.

Tim

[DummyLoad]

depending on which transformer cutouts you want.

http://www.mojotone.com/amp-parts/Chassis/Generic-Tweed-Super-Pro-Chassis-aluminum-rev-1

http://www.mojotone.com/amp-parts/Chassis/Generic-Tweed-Super-Pro-Chassis-aluminum-rev-2

with the two chassis in the above links, you have to machine the chassis except for the PT/OT openings.

another option would be to use a 5F6A bassman chassis and machine the three 9-pin socket holes to accept octal sockets. in either case get the dimensions of the PT and OT you plan to use and make sure they'll fit without machining or minimal machining.

HTH,

--DL

[fdesalvo]

Commenting to follow thread - def interested in this build. 

[HotBluePlates]

Can I ask why the interest in the 5B4 circuit?

As an aside, the 5C4 appears to be nearly identical, except for a 6800Ω resistor (5C4) in place of 7000Ω resistor (5B4) and the possible inclusion of an external speaker jack (according to Fender Amp Field Guide).

I ask because there are four input jacks, with one triode per jack. In my tweed-style builds, I haven't used more than 1 jack at any time unless I was jumpering the bright and normal channels together. I've gotten to where I don't like to pay for unused parts/channels, and unless you truly need 4 instruments plugged in, you could get the same results with fewer parts.

I also ask because the circuit of the 5B4/5C4 looks essentially identical to the 5B3/5C3 Deluxe, but with bigger output tubes and an extra speaker (and not the 5C3 Deluxe's feedback loop). So if you wanted "same but louder" it seems like some version of the 5B4/5C4 will work for you; if you want an alternative tweed tone, the 5F4 Super is truly cleaner/different while still being tweed.

I'm biased because I built a 5E3 copy and a 5F4 Super copy.

But back to your question

It looks like the WeberVST "5C3P Proluxe" might meet your requirements.

This is essentially a 5C3 Deluxe, no feedback loop, and 6L6 output tubes. It matches your intended amp except only 1 input tube is used to connect to all four input jacks instead of 2 input tubes. The "6N9P" tubes quoted are Russian octal dual-triode "6H9Π" which is a sorta-6SL7 equivalent. Doesn't matter to you except if you try to follow the layout.

Weber's 5C3P also alters the output stage to include fixed-bias, and slightly modifies the 5B4/5C4 paraphase inverter.

The chassis looks to use the same 5C3 Weber chassis. But to remain authentic, maybe you'll want the 5C5 chassis, which looks to duplicate the 5B4/5C4/5C5.

Sorry to be all stream-of-conciousness, but I was searching and typing at the same time.

[tubeswell]

The 5B4 and 5C4 V1 stages are in parallel pairs except for the grids - this would have the effect of the idle current in the 'unused' triode dynamically affecting the load line of the active triode. Merlin Blencowe describes this in the chapter on parallel stages his 1st book. (So its not the same as a 5C3 deluxe)

[HotBluePlates]

Yes, sorta.

Each input triode is grid-leak biased. So while the plate signals are mixed, it is unclear what (if any) effect one triode will have on another. The grid-leak bias causes each tube to settle-in on its bias in a very different way than in typical cathode-bias.

I haven't read Merlin's book, so I don't know if he raises points specific to grid-leak bias triodes which share only a plate load.

[olgoat]

The 5C5 Weber chassis looks like it will be perfect.  Thanks for the looking that up.  Mojotone had nothing and never thought of Weber.  Checked with Mission and they haven't done a run of those chassis' in years.

Thanks again.

TWC

Can I ask why the interest in the 5B4 circuit?

As an aside, the 5C4 appears to be nearly identical, except for a 6800Ω resistor (5C4) in place of 7000Ω resistor (5B4) and the possible inclusion of an external speaker jack (according to Fender Amp Field Guide).

I ask because there are four input jacks, with one triode per jack. In my tweed-style builds, I haven't used more than 1 jack at any time unless I was jumpering the bright and normal channels together. I've gotten to where I don't like to pay for unused parts/channels, and unless you truly need 4 instruments plugged in, you could get the same results with fewer parts.

I also ask because the circuit of the 5B4/5C4 looks essentially identical to the 5B3/5C3 Deluxe, but with bigger output tubes and an extra speaker (and not the 5C3 Deluxe's feedback loop). So if you wanted "same but louder" it seems like some version of the 5B4/5C4 will work for you; if you want an alternative tweed tone, the 5F4 Super is truly cleaner/different while still being tweed.

I'm biased because I built a 5E3 copy and a 5F4 Super copy.

But back to your question

It looks like the WeberVST "5C3P Proluxe" might meet your requirements.

This is essentially a 5C3 Deluxe, no feedback loop, and 6L6 output tubes. It matches your intended amp except only 1 input tube is used to connect to all four input jacks instead of 2 input tubes. The "6N9P" tubes quoted are Russian octal dual-triode "6H9Π" which is a sorta-6SL7 equivalent. Doesn't matter to you except if you try to follow the layout.

Weber's 5C3P also alters the output stage to include fixed-bias, and slightly modifies the 5B4/5C4 paraphase inverter.

The chassis looks to use the same 5C3 Weber chassis. But to remain authentic, maybe you'll want the 5C5 chassis, which looks to duplicate the 5B4/5C4/5C5.

Sorry to be all stream-of-conciousness, but I was searching and typing at the same time.

[olgoat]

As to why the interest, I love the full sound of this circuit compared to the later revisions.  I know the grid leak bias is probably a noisier way to go and I understand the amp is more sensitive to surrounding electrical activity like lights and dimmers etc.

Thanks

[tubeswell]

... unclear what (if any) effect one triode will have on another. ...

If one triode remains idle, it is conducting a steady amount of current, pulling the plate voltage (on both triodes) down, so the load line is pulled down. However when the other triode has a signal the load line moves, because the current changes through the shared plate resistor (because as the active triode's plate current decreases, the effect of that triode on the load line is taken out of the circuit, and the load line reverts to what it would be with one triode). And so it goes on, with the load line shifting back and forth, altering the operating point of each triode, depending on which triode is getting or not getting a signal. That's the gist of it from Merlin's book anyhow.

[olgoat]

Is that the "Designing Tube Amps" book?

[HotBluePlates]

That's kind of like looking at it under a microscope.

I say that because, unless you're playing through the "unused triode" what result happens that you can hear? And if you are playing through both triodes sharing a plate load, then we already know the output signals are mixed due to the shared load.

In my opinion, it's a non-issue that really doesn't contribute to the sound of the amp. The grid-leak bias being relatively unable to accept large input signals is more likely to dominate the situation.