SF Bassman to AC30 style amp conversion possible?

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fevzay
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SF Bassman to AC30 style amp conversion possible?

Post by fevzay »

Apologies in advance....newbie here. Been dabbling with a few old Bassman heads, and I am considering trying to turn one into a single channel Top Boost front end into a pair of cathode biased 6L6's.

Would this "work?" I am a newbie with more ideas than knowledge, so I'm not sure.

The OT has a 4K primary impedance. Will a pair of cathode biased 6L6's jive with this? Additionally, I am considering getting a Hammond tranny to have 4-8-16 ohm outputs in order to do the 2x12 thing in series.

Where should I begin with biasing them...what values? I'm still learning basic things like this out. No too worried about the layout or the implementation.

I have more questions than answers. Seems like the PT is too hot (340-0-340). Is it possible to add a dropping resistor off of the bias board getting me down to 280-290?
Last edited by fevzay on Wed Nov 08, 2017 2:54 pm, edited 2 times in total.
fevzay
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Re: SF Bassman to AC30 style amp conversion possible?

Post by fevzay »

DELETE
Last edited by fevzay on Thu Aug 02, 2018 12:43 pm, edited 1 time in total.
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xtian
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Re: SF Bassman to AC30 style amp conversion possible?

Post by xtian »

A significant part of that Vox top boost sound is the EL84 output section. You’ll get only part way there by grafting the top boost preamp onto a Bassman output section.

That said, the Trainwreck Rocket schematic and layout is simple, tested, and ready to roll if you want to try it!
I build and repair tube amps. http://amps.monkeymatic.com
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pompeiisneaks
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Re: SF Bassman to AC30 style amp conversion possible?

Post by pompeiisneaks »

Agree with xtian 100%

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fevzay
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Re: SF Bassman to AC30 style amp conversion possible?

Post by fevzay »

Thanks for the responses so far!

This idea is sort of inspired by an amp I had a while back, Top Hat Super Deluxe Mk2. It ran cathode biased by octal tubes (6L6, 6v6, 5881 AND EL34). The 5881 and 6L6's got close to my ears. It also has a Tweed/AC30 front end. Going to give it a run, I guess. Will have to play around with the bias resistor and cap values a bit.
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martin manning
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Re: SF Bassman to AC30 style amp conversion possible?

Post by martin manning »

Regarding resources, Merlin Blencowe’s books are good, and if you browse his Valve Wizard web site you can pick up a lot. If you like his style, get the books for the gory details. They are a very good value too. That would be Morgan Jones, BTW ;^)
tubeswell
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Re: SF Bassman to AC30 style amp conversion possible?

Post by tubeswell »

Old Bassman heads will retain more of their investor value if they are left unmolested. Why don't you sell one (or more) of those heads and buy an AC30 instead?
He who dies with the most tubes... wins
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M Fowler
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Re: SF Bassman to AC30 style amp conversion possible?

Post by M Fowler »

I build Steve Ahola's Tweed Hot Rod for some of my local guitarists, it's a very good tweed tone 50w amp.
hrt_bms7.pdf
hrt_lay1.pdf
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