1976 Boogie SP3 restore help

[electric mayhem]

Does anyone have pics of a close to stock Boogie with a SP3 board?

I need to order some parts for a couple amps I'm working on so I brought out my project A70x to see what I need to bring this thing to (hopefully) life.

As you can see it is not stock and I've never owned the OG to know what originally belongs but there are some things that seem obvious changes. I got it as a non-working amp and you can see I've swapped out the e-caps and all the .1uF orange drops that were actually "brown drops". I still need one more polypropylene.

 

[electric mayhem]

On the SP 3 there are 3 things that stand out.

There is a black (sprauge?) .047 cap and a Mullard tropical fish poly cap. Is it safe to say these were tone upgrades from original? Did Mesa ever use tropical fish?

The other thing are the light blue resistors. They are marked 100k 196T1 7619 and appear to be in parallel. At 1st I thought someone was trying for 50k ohms and only had 100k R's handy but if 7619 is the date they were made the same year as the amp.

 

[electric mayhem]

Reverb looks to have been added after the fact. You can see the 12V socket is white instead of black and I'm betting they had RP boards for stock reverb.

Not sure what the W and R stand for or purple/orange color coding.

 

[electric mayhem]

Someone really went to town on the "superiority" of film resistors. Currently on the PS board there is a 2W that I'm assuming has a faded red and is supposed to be 1k ohm, what looks to be 5.8k (1W) and 2 parallel R's 100K || 5.8k = 5482 ohm. The parallel resistors look like 1/2 watt and I assume this was done to up the power rating to 1W.

I think it's pretty safe to assume these should be two 1 watt 5.6k and one 2w 1k ohm but a confirm would be appreciated, of course all CC.

I recognize the 470 ohm screen R's on the PWR 3 board so I assume the screen and grid R's are the right value and just need changing to CC from the current film. Again, a confirmation especially on the grid is appreciated.

 

[electric mayhem]

It's anyone's guess if the OT blew or was simply changed but it has a Twin Reverb/Showman tranny. That may not be a bad thing but what OT was on a '76 H?
It's a Schumacher and the manu/date code looks like 606-5-32. I understand model 022889 would be 125A29A if it was 1965 so I'm guessing it is a '75 tranny.

It also seems to mean the amp is currently a 4ohm out so it might have a little more roar compared to stock.

 

[James]

I imagine the OT is a replacement. I have a 100w from the same year and it has the Mesa OT, but a different one from the later amps. Single 4 ohm tap. No 8-4-4 label on the back either.

I wonder if it did have factory reverb, but they were out of the RP boards that day. The transformer looks to be from the same era too.

 

[mark1406]

Okay, SP-3 is the number on the pcb. The brown drops might have been Mallory caps, I have seen them in Orange and Blue. I have seen pictures of a Mark 1 with brown Mallory caps.

In my late 70’s Mark 1 amp it had Sprague 418 caps. These are a polyester cap.

6PS/418 caps

The thing that has me scratching my head it the Bassman/Plexi P.I. stage. I put that into my SOB and the gain was ridiculous, there was no clean sound whatsoever.

Regards

Mark

 

[electric mayhem]

I imagine the OT is a replacement. I have a 100w from the same year and it has the Mesa OT, but a different one from the later amps. Single 4 ohm tap. No 8-4-4 label on the back either.

I wonder if it did have factory reverb, but they were out of the RP boards that day. The transformer looks to be from the same era too.

Didn't think about RP boards not handy. I guess that could have been a reality back then.

Do you have the part # for your '76 H OT? I'm curious what they used so I can keep an eye out for one. And does that mean the H was a 4ohm out in '76 or were there different configurations depending on what OT was used?

This amp has marker on the pre sockets and the 7025 marking V1, V2 and V3 looks to have been done by the same hand at the same time but V3 is the white socket. The power sockets changed from brown to white I think around IIC iirc but I've never paid attention to pre sockets.

The reverb tranny (022921 Schumacher) date is 831. I don't think they would be marking sockets 7025 in '88 so the tranny must be '78. I wonder if this was done at the factory in 78-79.

The PT is 100-62318 (606-632) and the choke's date 631.

 

[electric mayhem]

Okay, SP-3 is the number on the pcb. The brown drops might have been Mallory caps, I have seen them in Orange and Blue.

The thing that has me scratching my head it the Bassman/Plexi P.I. stage. I put that into my SOB and the gain was ridiculous, there was no clean sound whatsoever.

Regards

Mark

I'm sure I have some before pics somewhere with the brown drops around and I have all the parts I've pulled. Don't think I've seen the blue ones.

I've been reading up on different PI (tails etc.) and NFB but it's still settling in so can you explain which one the Bassman/Plexi is? Even better would be how you can spot it from the pics so I can learn how to see what you see.

I've been thinking most recently that this is a hot-rod of RCS's Princeton hot-rod. That black .047uF looks like what I see being called a "Black Beauty" cap. That black cap, the Mullard C280 metalized polyester which I hope is better than regular polyester I would choose polypropylene over, the Twin OT and what you are saying about the aggressive PI all point to someone juicing this thing up to be a tone fire-breathing Godzilla.

 

[Spinaltap11]

That's quite a amp you got there, i'm jealous

 

[James]

Didn't think about RP boards not handy. I guess that could have been a reality back then.

Do you have the part # for your '76 H OT? I'm curious what they used so I can keep an eye out for one. And does that mean the H was a 4ohm out in '76 or were there different configurations depending on what OT was used?

This amp has marker on the pre sockets and the 7025 marking V1, V2 and V3 looks to have been done by the same hand at the same time but V3 is the white socket. The power sockets changed from brown to white I think around IIC iirc but I've never paid attention to pre sockets.

The reverb tranny (022921 Schumacher) date is 831. I don't think they would be marking sockets 7025 in '88 so the tranny must be '78. I wonder if this was done at the factory in 78-79.

The PT is 100-62318 (606-632) and the choke's date 631.

I'll have to find out. I think it would have been a single 4 ohm output, but I do know the 9/77 100w I used to own had the 8-4-4 label and the OT was a slightly different size.

As for the caps, the brown ones are Mallory PVC

 

[mark1406]

I'm sure I have some before pics somewhere with the brown drops around and I have all the parts I've pulled. Don't think I've seen the blue ones.

I've been reading up on different PI (tails etc.) and NFB but it's still settling in so can you explain which one the Bassman/Plexi is? Even better would be how you can spot it from the pics so I can learn how to see what you see.

I've been thinking most recently that this is a hot-rod of RCS's Princeton hot-rod. That black .047uF looks like what I see being called a "Black Beauty" cap. That black cap, the Mullard C280 metalized polyester which I hope is better than regular polyester I would choose polypropylene over, the Twin OT and what you are saying about the aggressive PI all point to someone juicing this thing up to be a tone fire-breathing Godzilla.

In this picture of your amp you can see the 470 ohm cathode resistor. Two 1M ohm grid leak resistors, the 15K resistor, 56K feedback resistor, the 10K tail resistor which has a 10K presence pot across it.

The is a picture of the 470 ohm cathode resistor, two 330K grid leak resistors or a 330K and 1M ohm resistor per the circuit diagram, the 15K resistor, the 56K feedback resistor, and the 10K tail resistor.

The last picture is a 470 ohm cathode resistor, two 330K grid leak resistors, a 15K resistor, 820 ohm feedback resistor, and a 100 ohm tail resistor.

Regards

Mark

 

[electric mayhem]

Awesome - I really appreciate that. Looks like I'm heading back to robrobinette soon to review the PI types and see if I can insert this into my brain. If there is another good source for PI's I'm all ears.

Do you think this was original factory tinkering or maybe in or around '78 when reverb was added and potentially all the other tone caps/OT the PI got hot-rodded?

 

[electric mayhem]

You guys are correct on the brown Mallory 400V PVC caps.

Has anyone ever used polycarbonate film caps in their amps for their stability? If they were mil-spec back in the day I'm sure they cost more and maybe that is why they didn't get used?

V1 had these gold e-caps marked 22/25, 08.75 and with a J through H that reminds me of the Skinny Puppy moniker. Given the black beauty and tropical fish is this another exotic tone cap?

Either way one "SH" had an ESR of 30ohm which doesn't speak to good health and almost +30% uF value. And even tho I don't put faith in my cheap transistor tester's V-Loss display which I assume is a low voltage attempt at leak testing the 31% V-loss on the 2nd cap is off the chart from what I usually see.

 

[electric mayhem]

In my late 70’s Mark 1 amp it had Sprague 418 caps. These are a polyester cap.

I just re-read this. Were they at least metalized polyester? I'm pretty forgiving of old non-problematic filters but Idk if I would trust polyester film that old. Was it used for tone over longer lasting options?

I'm used to seeing 415's and 416's but now I'll have to pay more attention to see if I have any 418's that I'm not familiar with in any amps.

 

[James]

Those 25uf caps are stock. I had the same ones in the 76 I mentioned. I believe they are Siemens.

As for the modifications in general, I doubt it would have left the factory like that. Best guess is that someone attempted to make some improvements when replacing a blown OT

Looking closely, the outer two RCA jacks don't seem to be the usual type with the brown plastic. Two of the knobs on the back aren't the correct type either. Should be 0-10.

 

[electric mayhem]

Those 25uf caps are stock. I had the same ones in the 76 I mentioned. I believe they are Siemens.

As for the modifications in general, I doubt it would have left the factory like that. Best guess is that someone attempted to make some improvements when replacing a blown OT

Looking closely, the outer two RCA jacks don't seem to be the usual type with the brown plastic. Two of the knobs on the back aren't the correct type either. Should be 0-10.

Odd that they used those (should be 22uF, 25V) gold ones at V1 and different 22uF/25V the rest of the preamp. I replaced them all with 22uF/35V IC's. And I still need to lift a leg on the Mullard and Black Beauty to check if they are still in spec until I get a leak tester.

With the reverb tranny dated '78 you're right it didn't leave the factory that way originally but I've wondered if it made its way back to the factory 2-3 years later. I assume that was when the 7025 tube markings on the chassis were written. Idk when the 7025 spec was changed to 12ax7 but I assume it was late 70's.

The outer RCA's are the added reverb connects and the non-standard knob on back is the reverb pot. The slave knob does go 0-10 but someone put the silver innie back in the black plastic as an outie likely after it got damaged.

I should be getting the CC screen R's today. I haven't seen many examples but I've at least seen one original Mark on here that also has 2W film screen R's. It just seems that it should have been carbon comps originally.

 

[electric mayhem]

I got the new screen R's in. The film ones I pulled out measured from 470 dead on to 484ohm true to what you would expect from metal film.

I had closer value of the new CC's but had a quad of 502 ohm so I went with matched at +6.8% for the screens.

The grid 2.2k ohm R's measured 2.21, 2.19, 2.25 and 2.21k, all very good. I randomly pulled the PI cathode 470R which tested 481 ohm- great.

The .047uF black beauty came in at .059uF, 25%, but since I still need to order some .047uF polystyrene I put it back.

The mullard psychodelic fish tested at 9835pF = .01uF. With brown, black, orange, white, yellow I think it's within 2% assuming it to be 10k (pF) with yellow = 400v. That leaves white for a tolerance and while not often I've seen white for silver and yellow for gold on at least one chart.

I've been using bluebug's thread from last year for pics and the Mark I RI schematics. It looks like there is a .01uF there if I'm reading it right.

This amp has dual Dale 100k R's coming off V1A/B's plates where bluebug's has 82k there. With the Dale's being 1% I expect I'm close to 50k ohm effective compared to what I think is the stock 82k ohm R's. How is that extra V carrying from the V1 plates affecting the pre circuit?

 

[mark1406]

I wouldn’t use carbon composite for screen resistors, I personally prefer metal oxide as they are very durable.

Randall Aiken on resistors

I had carbon composite resistors in my Mark 1 amp and the resistor values drifted up as high as 2K, it’s amazing the CC resistors in your amp were so stable. Don’t order 0.047uF polystyrene caps (715/716) get polyester caps 225 or 6PS etc.

I’d be inclined to get rid of the four Dale resistors and just use 1 watt carbon film resistors. I have yet to see a You Tube clip where they demonstrate the tonal difference between resistor types. Carbon Composite resistors are notoriously noisy, you don’t want them in a high gain or early stages of an amp as the noise is amplified throughout the amp.

Coupling the signal from the gain stage to the normal input of amp is done with a 0.01uF cap. You can use anything from 0.001uF to 0.01uF in the amp. It depends on the bass response you are after.

Regards

Mark

 

[James]

For what it's worth, the screen resistors Mike B used for my IIB were the dark grey Vishay wirewounds. 470 ohm 3.75w

As for the reverb being factory, I still think it's unlikely. Certainly possible that it was modified/repaired more than once though.

Also, there's an SP-3 (August 1977) on amparchives. Can't tell much from the picture, but you can see what kind of components were being used. Looks like this one mostly has carbon comps