Masco MA-35 makeover

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dorrisant
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Re: Masco MA-35 makeover

Post by dorrisant » Thu Jul 20, 2017 7:48 pm

You are welcome and yes... that's where I get them. Coincidentally, I have a MA-35 here that I'm gonna rebuild for a customer. He is demoing an amp to see if that circuit fits his needs. I know I will need one of the Droppers in there too.
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pompeiisneaks
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Re: Masco MA-35 makeover

Post by pompeiisneaks » Thu Jul 20, 2017 8:05 pm

premiumplus wrote:
Thu Jul 20, 2017 7:30 pm
Very cool thanks a ton for posting that layout diagram, it looks like it can't be simpler. Is Mouser a good source for the MOSFET?
Looks like it to me:

http://www.mouser.com/ProductDetail/STM ... qarN8RU%3d
for the first one mentioned in his link and:
http://www.mouser.com/ProductDetail/ON- ... pGniNyk%3d
for the second :)

It also looks like this one by Infineon should do the needful:

http://www.mouser.com/ProductDetail/Inf ... 9KMVnE0%3d

but I've not compared the total specs, it just meets or exceeds the same ratings of the ones above, so I'd do some more testing/research before using it.

If anyone could confirm it works, I really like infineon's stuff, heres' the datasheet:

http://www.mouser.com/ds/2/196/IPW90R34 ... -71729.pdf

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xtian
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Re: Masco MA-35 makeover

Post by xtian » Thu Jul 20, 2017 8:27 pm

Yes, Mouser
I build and repair tube amps. http://amps.monkeymatic.com

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premiumplus
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Re: Masco MA-35 makeover

Post by premiumplus » Fri Jul 21, 2017 3:01 am

How do I go about buying one or two of those PC boards?

EDIT: on second thought, I'll just do it on stripboard.
Making the world a better place...one amp at a time!

gldtp99
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Re: Masco MA-35 makeover

Post by gldtp99 » Sat Jul 22, 2017 8:13 am

Why use the @70 year old PT and have to try and adapt it to the circuit you wish to build ? I've rebuilt many old PA tube amps for guitar use and I won't use iron that old just for general safety purposes.
You're building a guitar amp and that means someone (your friend) is going to plug an electric guitar into the amp and play it. Shouldn't user safety be more important than re-using the original PT ?

Proceed however you wish but here's one option for a new PT that seems to fit the type of circuit you've described------ Edcor makes many other models if you would prefer different specs:

http://www.edcorusa.com/xpwr008

Good luck on your project.

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dorrisant
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Re: Masco MA-35 makeover

Post by dorrisant » Sat Jan 13, 2018 2:58 am

Martin, From the first page...
martin manning wrote:
Tue Jul 18, 2017 2:52 am
In the schematic you posted, the first 6SN7 is the phase inverter. The tapped inductor is functioning as loads for the third 6SN7, which is driving the 6L6''s from its cathodes.

So the second 6SN7, is it a driver as well as the third? Looks like a regular gain stage between the PI and a cathode follower driver.

Also... would there be any advantage to keeping this arrangement in a conversion of this circuit? Possibly shortening it to two tubes, using something like a 6SL7 for the PI and a 6SN7 for the CF driver...? The 6SN7 has an amplification factor of 20 and the 6SL7 is rated at 70.

I would like to convert one of these MA-35 Ns to a Rocket-ish preamp. I'm wondering if it would be a good arrangement to feed the Rocket Preamp into a quasi SSS power section. Wondering if the tapped inductor should be kept. Maybe not with any mods to the PI section. This is a build for a touring musician and I wouldn't want to leave him out there with a critical part that may be unobtanium. He does tour Japan. :shock: He has on loan a big bottle Rocket-ish build that he absolutely loves. I wouldn't want to deviate too far from what he's playing now, but would relish the chance to expand my tube circuit knowledge.
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martin manning
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Re: Masco MA-35 makeover

Post by martin manning » Sat Jan 13, 2018 5:37 pm

dorrisant wrote:
Sat Jan 13, 2018 2:58 am
Martin, From the first page...
martin manning wrote:
Tue Jul 18, 2017 2:52 am
In the schematic you posted, the first 6SN7 is the phase inverter. The tapped inductor is functioning as loads for the third 6SN7, which is driving the 6L6''s from its cathodes.
So the second 6SN7, is it a driver as well as the third? Looks like a regular gain stage between the PI and a cathode follower driver.
It's a voltage amp, but the un-bypassed cathode resistor means the two signal paths will interact. Not sure what the point of that is; or perhaps it's not needed since the two signals are 180 degrees out of phase.
dorrisant wrote:
Sat Jan 13, 2018 2:58 am
Also... would there be any advantage to keeping this arrangement in a conversion of this circuit? Possibly shortening it to two tubes, using something like a 6SL7 for the PI and a 6SN7 for the CF driver...? The 6SN7 has an amplification factor of 20 and the 6SL7 is rated at 70.

I would like to convert one of these MA-35 Ns to a Rocket-ish preamp. I'm wondering if it would be a good arrangement to feed the Rocket Preamp into a quasi SSS power section. Wondering if the tapped inductor should be kept. Maybe not with any mods to the PI section. This is a build for a touring musician and I wouldn't want to leave him out there with a critical part that may be unobtanium. He does tour Japan. :shock: He has on loan a big bottle Rocket-ish build that he absolutely loves. I wouldn't want to deviate too far from what he's playing now, but would relish the chance to expand my tube circuit knowledge.
I guess I'd keep the inductor; it's not likely to fail. Finding octal preamp tubes might be the larger concern. I think it would be wise to listen to it before changing the topology. For guitar, you want some overdrive, which might happen naturally given that it's set up for mic input. You could cascade the input stages too.

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