alternative to restoring trashed Bassman head

[lexington125]

There have recently been a few thrashed and trashed bassman heads for sale in my area. Heavily modded, replaced parts, stripped to bare wood, etc. The good news is that means they are available at prices not seen in many years.

Assuming one of the two preamp channels is still mostly stock and functional (either “Bass” or “Normal” channel), would either of these heads be a good candidate for an upgrade? I was thinking of something like one stock input channel, with upgraded power and output transformers and a pair of KT88s. I wouldn’t even connect the other channel – I never understood the need for two channels for bass? As far as features are concerned, I just need one input, one volume control and the existing “bass’ and ‘treble’ tone controls; nothing else required. Two speaker outputs on the back side and I’m good to go.

The ultimate goal here would be a compact tube amp head with the stock Fender preamp and the output power ranging somewhere between a Sunn 200s, a Fender Showman or an Ampeg V4b. Something suitable for blues gigs in local bars / small clubs. (think 1960 Howlin Wolf or 1966 Booker T & the MGs, not Cream, Allman Bros or other heavy blues-rock)

I would almost certainly contract out the actual design/build work, but I want to do a little research and determine if this is feasible, realistic and if there are any similar projects documented online someplace?

Has anyone crammed larger transformers and a pair of KT88s in a Bassman sized head cabinet?

[eschertron]

I can't answer your engineering question ("Has anyone crammed...") but I feel compelled to observe that if you intend to toss the most expensive components from a bassman head (PT & OT) then why not simply contract somebody to build to your needs without forcing them to start with an old box and some rusty screws? If you want to use the head cabinet "as is" to evoke certain vintageness, then I understand. And you might be able to score the cab all by itself for less than the heads that are available, or offer your builder all the innards as partial compensation.

Still, I would start from new materials (chassis, sockets, etc) for the construction if you are already going to use new trannys.

[52 Bill]

I'm not certain what transformers are available for KT88 designs, but I've fit parts for 4-6550s in one. There are only a few inches difference in width between a Bassman and a Showman head.

As for the two channel question, when these amps were designed, it was fairly common for one amp to be used by more than one instrument at a time. So the bass player and the accordianist or the guitarist would both plug into the same amp. The world was a much different place back then.

[J M Fahey]

upgraded power and output transformers and a pair of KT88s.

Not realistic.

Getting an old bashed head is good because you can consider it the most expensive part of a kit: a chassis, cabinet, sockets, transformers and some hardware: pilot light, power switch, etc.

If you discard transformers, you are discarding the most expensive part, and keeping a battered rusty chassis, burnt torn stained Tolex cabinet, etc.
What's the point?

In that case get just a new kit , everything new, and build it.

Or get the Bassman, use 90% of it, just add/rewire/repopulate the original eyelet board (or fit a new one there).

[Justin Thomas]

I vote with the others. Personally, I'd make a 50W Bassman out of a trashed head... they're great amps. Just do an AB165 or later & jump the channels. Change cap & resistor values to taste, but for the most part, restore it to its former glory. One, the design works, two, these can be a secret weapon in any amp arsenal. Also, given the sound and influences you named, bet they used 6L6-equipped Fendery amps, probably 50W. Match a Bassman with a REAL speaker (not a plastic/rubber woofer "bass" speaker) and it'll do dang near anything.

Or you can just send the trannies to me for a nominal cost; I mean, it IS a great deal, right?

Justin

[lexington125]

I can't answer your engineering question ("Has anyone crammed...") but I feel compelled to observe that if you intend to toss the most expensive components from a bassman head (PT & OT) then why not simply contract somebody to build to your needs without forcing them to start with an old box and some rusty screws? If you want to use the head cabinet "as is" to evoke certain vintageness, then I understand. And you might be able to score the cab all by itself for less than the heads that are available, or offer your builder all the innards as partial compensation.

Still, I would start from new materials (chassis, sockets, etc) for the construction if you are already going to use new trannys.

I didn't go into the exact detail of the existing heads, but neither has both original transformers. The reason I was considering this idea was that these heads were already in "Frankenstein" condition, so they were cheap and so far gone as to make restoration to original almost hopeless.

[lexington125]

As for the two channel question, when these amps were designed, it was fairly common for one amp to be used by more than one instrument at a time. So the bass player and the accordianist or the guitarist would both plug into the same amp. The world was a much different place back then.

Oh, I get it as far as why they were originally designed that way; I just don't see a lot of utility in rebuilding one with both channels.

[lexington125]

I don't think either of the existing heads have both original transformers. It was their random parts condition that made this seem like a good idea.

re: new kit - I don't know anyone who offers a super simple, single channel, high powered bassman kit? I have seen a few 100 watt clones, but always built w/ 4ea 6L6, never a KT88 based amp.

[lexington125]

After a lifetime of playing tube bass amps (40 years +, and only 1yr without a tube amp), I know from personal experience that for me, a 50 watt bassman is right at the line of working / not working in a band situation, at least if you want to keep the speaker size/quantity within reason. On the other hand a Sunn 200s, which was only rated at 10 more watts (60 watts in old Sunn catalogs) was enough amp even in louder, more rock type bands.

I can't explain why a 60 watt Sunn 200s (2ea KT88 and HUGE transformers) was so clearly louder and more powerful than the 50 watt Bassman amps (2ea 6L6 and very nice, but a good bit smaller transformers). But I don't think you'll find many guys who have experience with both amps that won't tell you that the Sunn head just had more thump, a LOT more thump than you would expect from a 10 watt difference in output. I would not normally consider tearing a bassman apart to create a half-assed version of a Sunn 200. But these two heads I saw for sale almost beg you to put them out of their misery with a bullet to the chassis. Instead of a mercy killing, I was considering experimental surgery; but it seems most of you would consider it medical malpractice

[Justin Thomas]

I don't think it's medical malpractice, just an unjusyified expense. If you'te not worried about cost, go for it. But can you hold out hope for a trashed something else? I guess I'll alter my position - don't BUY new trannies. Just actively hunt for something that will power them. Heck, if the trannies were already replaced, maybe they'll power 2xKT88s? Post links to the sale? If you need the extra heater current alone, just get the auxilliary transformer for that. So, questions:

What kind of volts does the Sunn run at, and would the existing trannies in the heads put it out?
Post Sunn schemo?
Would the seller be willing to let you see if the PT puts out higher voltage, if needed?

Justin

[eschertron]

But these two heads I saw for sale almost beg you to put them out of their misery with a bullet to the chassis. Instead of a mercy killing, I was considering experimental surgery; but it seems most of you would consider it medical malpractice

If what you're looking at is already at the 'for parts' stage, then that's great! I don't think it was made clear in the original post. Most of the advice I've read here is simply to not buy more than you need, or don't kill a living patient for the sake of experiment

Your later posts make it clear that you do have a good idea of what you want; what is available. Thanks for that.

[loudthud]

The original Sunn 200S (2xKT88) runs a B+ around 500V with a GZ34 rectifier. Later versions (2x6550) ditched the GZ34 for silicon diodes and B+ shot up to around +550V. Power rating went up to about 80W.

Edit: A Showman makes a great sounding bass amp.

[Leo_Gnardo]

There have recently been a few thrashed and trashed bassman heads for sale in my area. - - - snip - - - Has anyone crammed larger transformers and a pair of KT88s in a Bassman sized head cabinet?

Hold out for a thrashed and trashed bassman 100 or 135 or Showman. Not all that much bigger than a standard bassman head. If you must, yeah you can cram all that into a standard Bassman, say remove preamp tube sockets V3 & V4, swap 'em out for octal, bolt in a 100W OT, maybe chip away a bigger hole for the PT and mount a bigger one there too, Twin-size.

[olddawg]

If the cabinets and hardware are complete and there are working transformers (replacement or not) it seems to me, as said before, it isn't that expensive to repopulate a tag board with new components even if you have to start from scratch. Then you could sell the 2 working amps and buy what you want? That's if you have the time and you enjoy doing it.

[lexington125]

Then you could sell the 2 working amps and buy what you want? .

I really wish that "what I wanted" existed someplace for me to purchase! That's why the idea of 'hot-rodding' an otherwise hopeless Bassman seemed like a good idea. For what its worth, here's what I want / can't find -

• simple, basic, single channel tube bass amp (head only)
• single volume control, no master
• simple tone controls (bass & treble, or bass, mid & treble)
• [NO sweep freq, or boost/cut switches, etc.]
• no FX loop, built-in FX or other add-ons
• 2ea KT88 output tubes and transformers capable of getting all you can out of these tubes

The easy way to communicate what I want is "a Sunn 200s" in a Bassman size enclosure. (if any of you aren't familiar with the Sunn 200s, there is more than one foot separating the power transformer, tubes and output transformer. The head enclosure was sized to fit evenly on top of their 2-15 cab and was at least 6" to 10" wider than necessary. Remarkably, when they beefed up the output section for the Sunn 2000 model, they made the head case even larger; I believe the 2000 was the largest amp head enclosure ever offered by a major manufacturer and it was approximately the same size as my first apartment in Boston.