Valco National 1201 1202 Sportsman

[bmccowan]

Several years ago I rebuilt a National Sportsman 1201, which is also often identified as a 1202. Valco, like Gibson had no respect for numbers!
Roarshock asked if I had a schematic, as he is thinking of building the circuit. I never found an original but drew one up from my amp. After replacing the caps, the mic channel sounds great. The instrument channel lacks the gain needed to drive the tone stack and is not strong enough to defend itself. I thought I had made a mistake, but searching out other owners I found they all had the same experience. If I wanted to mod it, I would adjust the tone stack or make it a one channel amp cascading the two sides of the 6SL7. I am not likely to mod mine, as I just consider it too cool for school, but maybe some ideas for Roarshock?

[roarshock]

Thank you for sharing your work!
Would you be alright if it ended up in the schematic library here? After my hunt for it, it'd be cool if others could build (or repair) their dreams. You were right that National played a little loose with their numbers. The insides of the only 1202 I could see showed 100k pots. Having a starting point like this for a build is wildly helpful.

Is the instrument channel just to clean for your liking or is it also significantly quieter than the mic channel too?

[bmccowan]

Happy to share and happy if it ends up in the library. Some other oddballs I've worked on have ended up there.
Sharing is what the Forum is all about.
Funny - I have seen the 1201 and 1202 models numbers attached to a single ended 6v6 1x8, a parallel SE 2x6v6, the circuit shown here, and a 2x6L6 with 2x10" speakers. It's like they could only count to 2.
The instrument channel lacks both gain and volume compare with the mic volume. I think going with a different T&B tone stack or increasing the resistance of the 10K tail resistor could go a long way toward bringing that channel out of puberty.
I think there is no real magic in this circuit, other than the use of the 6SL7 in V1. It's my favorite preamp tube.   

[dogburn]

I have to say that amp looks super cool - if I had an original one, I would definitely try to keep the circuit intact. But for building one based on it, I'd be inclined to do a single channel and cascade the two 6sl7 triodes. Would that be too much gain?

[bmccowan]

I have to say that amp looks super cool - if I had an original one, I would definitely try to keep the circuit intact. But for building one based on it, I'd be inclined to do a single channel and cascade the two 6sl7 triodes. Would that be too much gain?

Hey Dogburn - That is what I suggested to Roarshock. Lots of amps are designed that way, so no, not too much gain IMO. If it is, easily adjusted with the preamp plate resistors and the bypassed cathode resistors and caps. I love the clean sound of 6SL7s. I know the specs are similar to a 12AY7, but somehow they are just sweeter. Could be my imagination, no blind tests here.
I built a single ended "1947" Valco that is 5Y3/6SL7/6V6 with a 10" speaker - its a sweet thing.

[passaloutre]

I'm with you on the 6SL7! Though lately I've been using the "Loctal" 7F7 version, converting a couple old PA/HiFi amps to Tweed Deluxe variants with the full suite of Loctal 7F7-7C5-7Z4. As far as I can tell the 7F7 internals are identical to a 6SL7, but they are available NOS or JPO (just-plain-old) for pennies.

Anyways, maybe its psychological but these octal/loctal preamp triodes do sound sweeter to me

[bmccowan]

Hey, the vacuum is bigger, eh?
I've got a couple old Masco's and Flot-a-tones with those Loctals. Haven't messed with them yet. Ha, I'm 72, its about time eh?

[passaloutre]

Oh you don’t want to mess with the Loctals! I’ll be happy to take those amps off your hands