Mark 2c+ - Guts shot questions - Boogiebabies

[Thaymz]

Hi All

I took some photos of the internals of my c+ when I was transferring from combo to head. For any of the c+ experts out there, and / or boogie babies, is there any insight you could provide as to what I have?

Based on the serial number (mid 13,000s) and some of the internals I know its a 105PT DRG. Are you able to provide any more info for:

- Date? Given it says 38 from what I read this is 38th production week? Are there any other date indicators? I didn't see anything hand written on the board as mentioned on the guide for dummies
- Is there any evidence of mods?
- Tubes? I can see they are 2 6L6 and 2 34s but can't quite make out any branding if any. Do these fade over time?

https://flic.kr/s/aHsmspmz2N

Thanks in advance for any help! Best amp I've ever played, hands down.

 

[jrb32]

Boogiebabies doesn't really come on here much. If you can stick some photos up (https://imgbb.com works well) then I can have a look but to answer your main questions:

Based on the serial number (mid 13,000s) and some of the internals I know its a 105PT DRG.

It'll be a 105 if the transformer has the mark '105' stamped on it. But yes it should be a 105PT if it's a DRG. Some photos will help though.

Date? Given it says 38 from what I read this is 38th production week? Are there any other date indicators?

Yeah if it has DRG 38 written on it it'll be the 38th week of that year. Given the short period they were produced, and that the 38th week of the previous year they were still making Cs, and the 38th week after that they were making the IIIs, it'll be a 1984 amp from the 38th week so September 1984. Usually there is a date code hand written in sharpie where the 12ax7s plug in but not necessarily.

Is there any evidence of mods?

Stick some photos up and I'll have a look

Tubes? I can see they are 2 6L6 and 2 34s but can't quite make out any branding if any. Do these fade over time?

Again some photos would be great. The original output valves are generally pretty solid (STR 415s for the 6L6, unsure for the EL34s) and in working condition would be sought after highly. Unless the amp has been toured massively they will be fine.

The EL34s have a tendency of blowing. Loads on info here:

http://forum.grailtone.com/viewtopic.php?f=16&t=41938

 

[Thaymz]

Hi

Thanks for the info. Yes sorry I initially put a link from iCloud but it had some personal details so I removed it. Replaced with the flickr link once I managed to upload the photos there.

IMG_0225

IMG_5129

IMG_1653

IMG_7992

IMG_6956

I've just had another look and it turns out the 6L6s are Mesa STR 454's. No markings on the 34's though so no idea on those. To that, ignore the tubes question. Now that I know what I have I'll check online for difference.

Cheers
Themi

 

[jrb32]

I've just had another look and it turns out the 6L6s are Mesa STR 454's.

Decent valves! Info here https://www.watfordvalves.com/product_detail.asp?id=1814
People rave about the Philips/Sylvania Winged Cs as a decent IIC+ valve rather than the Svetlana but I'm not an expert in these.

One of your 12AX7s is bent but I'm sure you've corrected that - easy to bend back.

Board looks stock! I'm not sure on those 4x 220uF filter caps though (the four big grey ones) if they're original? But I'm guessing they are probably stock. Do they say Mesa USA or BMI? If so they're stock. Either way if you don't know the history of the amp, do a full filter cap job (4x220uF + 4x30uF) and bias cap job (2 x 47uF axial caps) and upgrade the 2W 680 ohm resistor nearest the 3x30uF caps on the RP11 board to a wirewound 5W. All these you can get from Mesa directly. DO NOT GET THEM FROM ANYWHERE ELSE! Their caps are original high quality and decently priced and 100% the right caps for your amp that way. If I ever found a C+ with non Mesa filter caps I'd replace them with Mesa ones immediately.

Yours has the RP11A board, so from that year and serial yours is a stock C+, not a C to C+ upgrade. They have slightly different values to an RP10A that was upgraded from a C to C+ and will sound slightly different to these.

Also check the resistance of the 4x 2W 470 Ohm resistors on the PWR board going to the output valves. These blow all the time especially if you don't know the history of the amp and an output valve has ever blown. Worth checking anyway as these may need replacing (again I use wirewound high W versions)

Send it to Mike B for a full service if you can but if you're outside the US then a competent amp tech can do the above no problem. Those are the main things to check.

Hope that helps!

Thanks

Jon

 

[Thaymz]

Thanks for the info Jon, really appreciate it!

Yes I did fix the alignment on the 12AX7s before moving the chassis in the head. Glad to know it's stock with no mods! I was fairly confident on it being the RP11 and stock c+ given the serial number and Pull Deep on the faceplate.

By the 4 grey large ones do you mean the couple at the back near the GEQ? If so, I think I can see Mesa USA on them under that tape when I zoom in.

I live in Aus so will need to take to a tech near here if I want to get re-capped. For now, I'll leave as is since there doesn't seem to be any issue with it and I think it goes without saying that I trust the local Mesa tech far less than MB with this amp. So will only take it there if there's a solid need to.

On the tubes - I may seek out some of the STR415's. Would it be fine if I buy a matched quad set but keep the 34's on the outer tubes?

Also have you had much experience moving from combo to head? I found I couldn't keep the fan power cord plugged in to the amp when sliding the amp into the head. There was barely any room between the PT and some of the framing in the head so I ended up having to leave the reverb out so I could use that reverb cavity underneath to then plug the fan cable after I had installed the amp into the head. I suspect this headshell was from a mark 3 or mark 4 which would've needed less room for the PT and therefore would've fit the amp chassis with the reverb power plugged in into the space where you slide it it. I'm not sure if that makes sense, it's hard to describe. If understood - Is this common? It's not a huge deal since I use the axe fx for effects but would've preferred it all in there.

 

[kc_ksom]

Cool amp mate - what part in Australia are you from - I would recommend just going to Pro Audio in Canberra they are the dealer - the tech there is very cluey, he may want to replace all the components though? - there is also another guy here on the forum that posts by the name Mcbarry he is also very cluey - there is also a guy here in Brisbane - B J Amps - I have used B J amps 3 times and his rates are very cheap and he does seem to do good work - he does not scare when you say boogie but in saying that I still had the same issues after he fixed mine - could have been an over site but there was a blob of solider that was shorting out intermittently causing crackling etc, twice it caught fire for a short second and burnt the screen resistors etc - that has since been fixed but I believe he created another issue when he replaced an LDR - it sounds like he may have put it in the wrong way around, I have not checked this as yet so I cant confirm if that is in fact the problem, so I don't want to bag anybody.

Casey

 

[Thaymz]

Thanks Casey, I'm in Melbourne. I had a fairly lengthy chat with the main guy from Pro Audio and would send the c+ to him if it needed anything. He mentioned he knew Mike personally so I'd have comfort that if he wasn't sure what to do he'd get on the phone to Mike to confirm before doing anything.

The main authorised Mesa repair guys here are Logitronics and I've had my V in there a couple times and they've done good work. Not cheap, but the V has a lot going on so I don't expect cheap and I'd keep going to them for my V. Given the rarity of the c+ I'd rather either Mike do any work - or second best someone that would speak to Mike to find out exactly what to do.

 

[jrb32]

Use a decent temperature controlled soldering iron to not damage the board (I set mine around 410 degrees C for old boards that use leaded solder). Oh and use lead solder.

Apart from doing the maintenance stuff I listed about where you can get all the parts from Mesa, basically leave it alone unless anything is obviously broken or you wan't something changed about it (brightness reduced, EQ pop fix etc).

Simply for maintenance, get all parts directly from Mesa. Replace:

4 x 220uF 300V Filter Caps
4 x 30uF 500V Filter Caps
2 x 47uF 100V Bias Caps
1 x 680 Ohm Resistor (wirewound 5W) to replace old one.

Apart from that check the power tube 2W resistors and the diodes with a multimeter and replace if necessary.

Job done But I agree you don't want some cowboy ruining your board or doing a poor job or anything! The Mesa recommended people should be fine (Logitronics). The Pro Audio guy I can't comment on but it sounds like he can't put an LDR on the right way round so I would be cautious especially if he wants to start swapping everything... if Mesa say a place is fine then go there and tell them exactly what you want done as above and it'll be fine. You can always call Mesa for reassurance.

 

[Henz]

Nice amp! I see it doesn't have the bright reduction mod. And the 120 pf cap is out on the V2A too. What does that cap do anyway? Why was it taken out?

 

[Thaymz]

Nice amp! I see it doesn't have the bright reduction mod. And the 120 pf cap is out on the V2A too. What does that cap do anyway? Why was it taken out?

Not sure man, far too technical for me.

I found this on the guide for dummies, perhaps this is the reason?

“Update:

The dark brown preamp resistors that look like 1/4 watt are 1/2 watt Beyschlag.
After August 1984 the 120pf cap from the grid to the cathode on V2B was removed. This is the effects loop signal, lead master and reverb output
from V2A.”

 

[Henz]

That's ok brother. For starters there would be a 1000pf 1kv cap in parallel with the 270 plate resistor on V4A. Thanks for the info. I still want a detailed reason why that 120pf cap is there. Mine still has it and my amp is a very early C+.