"Bass-Wreck" or "Wreck-Man" Updated

[Bob-I]

Thx everyone for the great comments on the layout thread. I figured I'd let that one take a life of it's own. Turned out to be a wealth of information.

I purchased a modded SF Bassman that I plan to use as a donor for this amp. The PT has been replaced but the OT is original.

I used the Fender Bassman layout that used to be on schemheaven, the express board posted here, and reversed it to match the Fender chassis. After I drew in all the components I removed the layouts and ended up with this. I'm mission some obvious stuff, grounds, B+, xformers etc. The cap board will go in the doghouse as per Fender, which ends up surprisingly close to the diodes and B+.

Comments?

Thx

UPDATE

I've added some of the suggested changes. Note that there are now 2 inputs, #1 uses just one triode, #2 uses both. I moved the 1K 25W resistor off the filter cap board, increased the first filters to 160/350 x 2, and added the PPIMV, changed the NFB to 47k. Plus I completed many of the incomplete things.

[paulruby]

Looks great...

[John_P_WI]

Bob,

I've done a lot to these amps. First check your bias wiring on your drawing, rewire it to blackface spec.

You should have 425 v or so on the plates. EL34s work too, yes the PT will get warm.

The OT is fine, but won't have the bone crushing bottom end like a Marshall. Also the 100k FB is a little tight with the 4 ohm tap, try a 47k.

You'll have a boatload of gain and might want to consider a PPIMV to enjoy it.

Also, I can't stand to see unused tubes (I know you are omitting one) but leave room on the tag card for v1b. I like to run v1a and v1b in parallel for thick tone (or in series for a monster).

John

[Normster]

First off, you've got to be the only guy I know who would convert a SFBM into a TW! (Cool idea, though. The ultimate sleeper.)

I would use both inputs rather than just one and wire them up Fender style. That way you have the low gain input for an additional gain option without compromising the circuit too much. Better yet, wire V1 to run a single triode or parallel triodes using each input and cascade V2 instead.

I think you're pushing the limits with that first filter cap. The Bassman PT will put about 440V on the plates. I think it would be safer to just put two 80uF's inside the chassis (maybe the 1K 25W as well). The doghouse won't be full, but you'll have safer filtering.

As for the leftover tube...and old SLO cloner like yourself would certainly know what to do with that.

[CaseyJones]

First off, you've got to be the only guy I know who would convert a SFBM into a TW! (Cool idea, though. The ultimate sleeper.)

No disrespect to Bob but I have one better... I dumped the solid state guts our of an old Squier practice amp and Wrecktified it! It's more like a mini-Liverpool than an Express in sheep's clothing.

There seems to be a lot of that going on with the Dumble clone guys. Apparently a Vibro Champ to mini-Dumble conversion is about the norm.

[John_P_WI]

Bob,

My current "favorite" amp is structured very similar to my previous post. One thing that I find that I need to tweak on this type of circuit is the .002 coupling cap into the 150k load resistor. Sometimes I will jump (parallel) the .002 cap with a ceramic 100-300 puff cap to pull out more mids. If there is too much gain, I'll split the 150 k load resistor into a 47k / 100k voltage divider too.

These bassmans are great amps to tweak...

John

[Bob-I]

Bob,

I've done a lot to these amps. First check your bias wiring on your drawing, rewire it to blackface spec.

I had it wired that way at first, then I changed it using the Express layout. I'm not really sure which is best for a nice quiet bias, but I don't like having the bias hanging from the wiper.

You should have 425 v or so on the plates. EL34s work too, yes the PT will get warm.

I guess you missed where the PT was replaced . All bets are off until I measure/check the specs.

The OT is fine, but won't have the bone crushing bottom end like a Marshall. Also the 100k FB is a little tight with the 4 ohm tap, try a 47k.

Thx, I forgot that this was 4 ohm only. I'll change that.

You'll have a boatload of gain and might want to consider a PPIMV to enjoy it.

Also, I can't stand to see unused tubes (I know you are omitting one) but leave room on the tag card for v1b. I like to run v1a and v1b in parallel for thick tone (or in series for a monster).

wire V1 to run a single triode or parallel triodes using each input and cascade V2 instead.

Both good ideas. What I've done in the past is use terminal strips to add ckts, then make a new card when I'm satisfied.

My current "favorite" amp is structured very similar to my previous post. One thing that I find that I need to tweak on this type of circuit is the .002 coupling cap into the 150k load resistor. Sometimes I will jump (parallel) the .002 cap with a ceramic 100-300 puff cap to pull out more mids. If there is too much gain, I'll split the 150 k load resistor into a 47k / 100k voltage divider too.

Excellent, notes taken

[Bob-I]

First off, you've got to be the only guy I know who would convert a SFBM into a TW! (Cool idea, though. The ultimate sleeper.)

All I need now is a faceplate that says "Wrecked-Bassman"

I think you're pushing the limits with that first filter cap. The Bassman PT will put about 440V on the plates. I think it would be safer to just put two 80uF's inside the chassis (maybe the 1K 25W as well). The doghouse won't be full, but you'll have safer filtering.

I'm concerned about that too. Thing is I HAVE all these Sprague caps and I don't want them to go to waste.

2 80's would only give me 40 total filtering. All the Wreck's I've seen have 80.

As for the leftover tube...and old SLO cloner like yourself would certainly know what to do with that.

[CaseyJones]

First off, you've got to be the only guy I know who would convert a SFBM into a TW! (Cool idea, though. The ultimate sleeper.)

All I need now is a faceplate that says "Wrecked-Bassman"

And maybe a cherry Bassman head cabinet?!

[doctord02]

A big part of the wreck magic is the PT voltage from what I gather; 440V DC will significantly change the sound. 395-405V DC is more like a wreck..

[Bob-I]

A big part of the wreck magic is the PT voltage from what I gather; 440V DC will significantly change the sound. 395-405V DC is more like a wreck..

Thx, I've gathered that fome reading here.

I'm thinking I may need to lower the B+. One of the reasons I bought this Bassman was the PT has already been replaced so I won't be bastardizing it more if I have to replace it again with a lower voltage PT.

[philmanatee]

I'm excited to see how this turns out. It would be cool if you could retain somewhat of a stock look, it would really freak people out when they heard it! Phil

[Bob-I]

I'm excited to see how this turns out. It would be cool if you could retain somewhat of a stock look, it would really freak people out when they heard it! Phil

How about I make up a BF Faceplate, Bassman logo changed to "BassWreck" and leave it looking old and beat up

[Bob-I]

No comments on the new layout?

[John_P_WI]

Hi Bob,

Looks like fun and you took everyones suggestions to heart.

I see that you are using the input jacks to select half of V1 or the other jack to select V1 parallel. Cool idea. (I usually just tie the grid pins together) I have used this technique to cascade an additional gain stage though.... This amp will be a real sleeper!

Seriously, if this is anything like the bassmans I have worked on in the past, even using good new preamp tubes (tung sol) and good EL34's (hope your replaced PT will handle 'em), you'll have sonic Nirvana.

John