2020 Monkeymatic Lassen #4 (1482)

[xtian]

Starting #4 in my series of "Lassen" small combos.

1. based on Supro 6424T with tremolo
2. based on Supro 6424, no tremolo
3. based on Supro, but with EL84 power section
4. based on Silvertone 1482, no tremolo, SS recto, EL84 power section

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EDITED 11/7/20

[Colossal]

Looks great, man! Love the layout, very short path. There's a lot of gain there.

[Phil_S]

Nice layout. Elegant. Let's argue about grounding. Kidding about argue, but want to discuss. I see you are grounding the filter caps at the artificial center tap for the heaters. I was under the impression that you shouldn't mix these together. Maybe because you introduce a/c heater hash into the B+ ground. My gut tells me I want to ground the filter caps anywhere but there. Curious, have you done this before? Problems?

[ViperDoc]

Thanks for sharing, xtian. Question from the class:

If I may, I see two parallel, identical triode stages heading into V2A—would this be considered a second or a third gain stage?—then hitting your V2B phase inverter and into your EL84x2 output. Is it the 68 K tail resistor that determines whether this is a “long tail” PI?

[xtian]

Nice layout. Elegant. Let's argue about grounding. Kidding about argue, but want to discuss. I see you are grounding the filter caps at the artificial center tap for the heaters. I was under the impression that you shouldn't mix these together. Maybe because you introduce a/c heater hash into the B+ ground. My gut tells me I want to ground the filter caps anywhere but there. Curious, have you done this before? Problems?

Yes, I've used this style of grounding in all my builds. My approach is to use two primary grounds to chassis. One for the "noisiest" current hogs: CTs, heater ground, reservoir filter, screens filter (because these grounds are grouped together, the current does not flow through the chassis). Second for most sensitive parts of the circuit: preamp stages, grounded far away from any potential noise.

Merlin says this, on the subject, "If the heater supply is not elevated but simply grounded then this connection can usually be made to any convenient point on the chassis, or else to a point close to the reservoir capacitor. However, heater hum is induced in many ways so it may be worth experimenting by making the connection to various points on the circuit ground to see if any particular place happens to give more favourable hum performance." http://www.valvewizard.co.uk/Grounding.pdf

[xtian]

I see two parallel, identical triode stages heading into V2A—would this be considered a second or a third gain stage?—then hitting your V2B phase inverter and into your EL84x2 output. Is it the 68 K tail resistor that determines whether this is a “long tail” PI?

I would say the two parallel triodes comprise a single gain stage. Then the signal hits a second gain stage (V2a) and then the cathodyne phase inverter.

[thetragichero]

besides having to order dual gang pots, I'm digging this. possible option for a Hammond ao-44 based build. thank you

[ViperDoc]

I see two parallel, identical triode stages heading into V2A—would this be considered a second or a third gain stage?—then hitting your V2B phase inverter and into your EL84x2 output. Is it the 68 K tail resistor that determines whether this is a “long tail” PI?

I would say the two parallel triodes comprise a single gain stage. Then the signal hits a second gain stage (V2a) and then the cathodyne phase inverter.

Thanks for the article!

[echuta13]

I've been doing my grounding schemes the same way and they work very well!

Rob Robinette goes over it a bit on his page: https://robrobinette.com/How_Amps_Work.htm

I try to localize my power caps in the circuit like xtian is doing too.

[Phil_S]

Merlin says this, on the subject, "If the heater supply is not elevated but simply grounded then this connection can usually be made to any convenient point on the chassis, or else to a point close to the reservoir capacitor. However, heater hum is induced in many ways so it may be worth experimenting by making the connection to various points on the circuit ground to see if any particular place happens to give more favourable hum performance." http://www.valvewizard.co.uk/Grounding.pdf

Yes, exactly my reference on the topic. I have taken "at any convenient point on the chassis" to mean not combined with any other ground. Perhaps I have read too much into that statement. Thanks for sharing your thoughts. If I do another build (sadly GAS seeems to have passed, pun intended,) I'll give this a try.

[xtian]

Friends, the little tube socket PCBs Lou and I made make wiring the heaters almost...pleasurable!

IMG_4610.jpg

The OT is going inside the chassis, as you see. It fits, and I "headphone tricked" it, and it has no hum in this position.

[sluckey]

I did a 1482 layout a few years back for an occasional Hoffman forum member. Never heard how it turned out.

http://sluckeyamps.com/misc/Silvertone_1482.pdf

[thetragichero]

are those boards available anywhere? i remember you posting these and they're friggin genius (especially for the non-belton micalex sockets i ordered by accident that tend to suck the solder into where the pins go)

[pompeiisneaks]

Yeah forum member does them:

https://luigiretro.com/LRC-VT9A

~Phil

[xtian]

All done wiring. I LOVE these noval PCBs. Each "leg" has two solder pads, making wiring super easy.

Will fire up tomorrow.

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