Hey guys!
Long time no see.. 🙂 Happy New year!
After several years of having this amp I finally pulled it out the rack, cause it suddenly became silent. Short tests showed that was a 5v rail related issue and the problem was simply a 1n4007 diode, that rectifiers 6.3 VAC for 7805 regulator. Without 5 volts input LDRs are open, thus no signal goes thru. After replacing it, the amp came back to life! But I thought it would be great to reverse-engineer this puppy, cause I still can't find its schematic whatsoever.. So, what the heck?! 🙂
And after 3 full days and 4 evenings I've finally done drawing. Here it is:
https://drive.google.com/file/d/1bzIvRelnxfL81XCXtqnjrrWVkSMnSQSL/
There are:
1) Different photos of the amp's guts.
2) PCB file, drawn in Sprint layout 6.0.
3) DWG file with schematic.
4) PDF file with schematic.
Also I'm attaching the circuit diagram directly here for the easy of reference.
Later I'll measure all voltages and include em onto schematic as well
If you find something obvious - please let me know.
PS. Lemme tell ya, this amp is a mess... As any Boogie amp - getting PCB out is a HUGE pain in the a... neck - desoldering is mandatory - I guess connectors are not a solution for Mesa.. LOL
One thing, that caught my eye, is channel A shielded cable is tided up together with AC mains input line.. Hmm.. is it strange? Also no AC wires are twisted at all. Of course, there is no instrument level signals, but why, Mesa?
PS.PS. I've been still figuring out the ac mains portion of the pcb layout - so take it with a grain of salt.
Cheers, Phil.
Long time no see.. 🙂 Happy New year!
After several years of having this amp I finally pulled it out the rack, cause it suddenly became silent. Short tests showed that was a 5v rail related issue and the problem was simply a 1n4007 diode, that rectifiers 6.3 VAC for 7805 regulator. Without 5 volts input LDRs are open, thus no signal goes thru. After replacing it, the amp came back to life! But I thought it would be great to reverse-engineer this puppy, cause I still can't find its schematic whatsoever.. So, what the heck?! 🙂
And after 3 full days and 4 evenings I've finally done drawing. Here it is:
https://drive.google.com/file/d/1bzIvRelnxfL81XCXtqnjrrWVkSMnSQSL/
There are:
1) Different photos of the amp's guts.
2) PCB file, drawn in Sprint layout 6.0.
3) DWG file with schematic.
4) PDF file with schematic.
Also I'm attaching the circuit diagram directly here for the easy of reference.
Later I'll measure all voltages and include em onto schematic as well
If you find something obvious - please let me know.
PS. Lemme tell ya, this amp is a mess... As any Boogie amp - getting PCB out is a HUGE pain in the a... neck - desoldering is mandatory - I guess connectors are not a solution for Mesa.. LOL
One thing, that caught my eye, is channel A shielded cable is tided up together with AC mains input line.. Hmm.. is it strange? Also no AC wires are twisted at all. Of course, there is no instrument level signals, but why, Mesa?
PS.PS. I've been still figuring out the ac mains portion of the pcb layout - so take it with a grain of salt.
Cheers, Phil.
That's amazing work Phil! I'm trying to get a 230v transformer for my 2:90 and can't even find a winder that will take on the job with knowing the currents for each winding, this led me here as they are to all intents and purposes the same amp. Would you know the model number of the mains tranny on your amp?
Thank you, MightyBassa!
Believe me or not, identifying xformer model numbers is a very nontrivial task in this amp - they buried inside of the chassis and not accessible without almost full disassembly, especially power tranny - it's even harder, than looking underneath the pcb! LOL.
I'll see what I can do, and let you know.
PS. Also I've corrected minor errors in the schematic. File is updated.
https://drive.google.com/file/d/1bzIvRelnxfL81XCXtqnjrrWVkSMnSQSL
I know, I had quite the mission unsoldering the wires from what was left of the melted plastic connector of course!
Then more fun getting to the 8mm securing nuts to remove the tranny only to find half the letters stamped on the endbell just happen to coincide with a fender tranny.
The other number sequence showed me it's a US tranny which I knew anyway.
At least it sounds good when it works...it's just the small issue of it looking quite pikey hooked up to a 3.5kva site transformer...the Mrs does not approve!
Then more fun getting to the 8mm securing nuts to remove the tranny only to find half the letters stamped on the endbell just happen to coincide with a fender tranny.
The other number sequence showed me it's a US tranny which I knew anyway.
At least it sounds good when it works...it's just the small issue of it looking quite pikey hooked up to a 3.5kva site transformer...the Mrs does not approve!
Fender sells its transformers for VERY reasonable prices to Authorized Service members, much better than, say, Heyboer, Hammond, etc. so many Techs get into Boutique Amp building using Fender Parts.
Maybe MB is doing something similar.
Iron quality is very good.
Maybe MB is doing something similar.
Iron quality is very good.
MB want $839 + post for an export tranny which seems a bit strong as I only gave £300 for the amp with seven good output valves and only minor fettling with dry joints and of course a re-cap session.
I spent a bit of time looking at fender tranny's and there is one that apparently has very similar voltages, if not exact..it was the current requirements for each of the taps (other than the heater of course) that concerned me.
I see where you're going though, there is a qualified MB service place nearby so maybe I should give that a go.
I spent a bit of time looking at fender tranny's and there is one that apparently has very similar voltages, if not exact..it was the current requirements for each of the taps (other than the heater of course) that concerned me.
I see where you're going though, there is a qualified MB service place nearby so maybe I should give that a go.
I can't think of a eight 6L6 Fender. And the way it is jammed in there is not helpful.
As a non-native English speaking person; I do not understand what #8 and #9 are telling.
explain: eight 6L6 Fender
explain: quite a tall order
I'm never to old to learn something...
explain: eight 6L6 Fender
explain: quite a tall order
I'm never to old to learn something...
Sorry if I have misunderstood what it is you want clarifying, I have a 2u rackmount amp with 8 6l6gc (4 a channel PPP) but it work on 117v not 230? And I'm looking for how to make a neat conversion without a step up transformer.
The mention of fender was related to the similarities with both brands so the transformers could be seen to be transferable? Mostly yes, but this particular amp, no, at least with the research I've done so far.
Because the amp is compact, the transformers are also all maybe undersized? So the "tall order" is more a slang/ informal recognition that what I ask is not completely normal.
For what it's worth, I couldn't get 8 or 9 to be legible viewing the site by my phone either.
The mention of fender was related to the similarities with both brands so the transformers could be seen to be transferable? Mostly yes, but this particular amp, no, at least with the research I've done so far.
Because the amp is compact, the transformers are also all maybe undersized? So the "tall order" is more a slang/ informal recognition that what I ask is not completely normal.
For what it's worth, I couldn't get 8 or 9 to be legible viewing the site by my phone either.
Last edited:
Oh, I understand now. Thanks for the explanation.
The site of "Ask Jan First", fragjanzuerst is'nt the most visualy appealing one.
8 and 9 refers to the links on the particular page
8 Custom made mains transformers
9 Toroid custom made mains transformers
A phone is a bit to small to see the page. Try a bigger screen.
Price is decent, Quality is cery good.
Maybe a bit costly to ship outside Europe...
The site of "Ask Jan First", fragjanzuerst is'nt the most visualy appealing one.
8 and 9 refers to the links on the particular page
8 Custom made mains transformers
9 Toroid custom made mains transformers
A phone is a bit to small to see the page. Try a bigger screen.
Price is decent, Quality is cery good.
Maybe a bit costly to ship outside Europe...
I'm in the UK so that's not such an issue, but until I know the current ratings of each winding, i am not going to get much progress, but that's ok,I've got one of the three windings current ratings down, it's just HT and bias I need to figure out...or repaint the 110v transformer with flowers..I'll have a look with a laptop tomorrow and see how it goes
It shouldn´t be difficult, just search a little:
* Fender amplifiers often use 6L6 power tubes.
2 x 6L6 for 40/50W amps, 4 x 6L6 for 100/135W ones, 6 x 6L6 for 180W ones, so an "8 x 6L6 amp" would mean an around 400W amplifier ... what we are talking about here.
* for idiomatic expressions you should search a dictionary, such as:
https://www.merriam-webster.com/dictionary/tall order
PS: just curious, what is your native language?
Lots of people from all over the World meet here 🙂
Buonas dia Fahey,
If you look backwards from your explanation; yes, it isn't difficult.
The other way round; yes it is.
Any way, I learned a bit of English.
Thanks
If you look backwards from your explanation; yes, it isn't difficult.
The other way round; yes it is.
Any way, I learned a bit of English.
Thanks