IIBornotIIB
Well-known member
IIB Coli’s are loose, wimpy amps with NO balls. And they cost a lot to put good glass in them. Plus they weigh a lot, and are very temperamental.
D
dr teeth
Active member
Touching back on the old Marks bias target and using the 6L6GC's 30W for I=P/V the 100% dissipation is 60 mA for 500 plate volts and 666 (x .1) for 450 plate V. It seems a forgone understanding mesa goes with cold tubes comparatively for bias so 70% dissipation is obviously not the "mark."
I've seen sites that indicate 50% as cold which yields 30mA for 500V and 33.3 mA for 450V. If high 20's is roughly the midpoint of the mesa tube rainbow it stands to reason that mesa might target 40-45% dissipation in general which for 450 plate volts is 26.7 - 30 mA. From there I have to guess they use their ears (or Doug West's ears) to dial in (likely on a temp pot they don't include in production) the bias point for the specific tube they built the circuit around, in our case the STR 415, or at some point the 454.
Mid-teens mA tubes for those plate volts puts dissipation in the low 20's. Of course less dissipation means tubes should last much longer up to some point of running way too cold.
For 7581A that same 450V translates to 35mA for 45%.
Has anyone here used 7027A's in a coli? If so, what brand?
I've seen sites that indicate 50% as cold which yields 30mA for 500V and 33.3 mA for 450V. If high 20's is roughly the midpoint of the mesa tube rainbow it stands to reason that mesa might target 40-45% dissipation in general which for 450 plate volts is 26.7 - 30 mA. From there I have to guess they use their ears (or Doug West's ears) to dial in (likely on a temp pot they don't include in production) the bias point for the specific tube they built the circuit around, in our case the STR 415, or at some point the 454.
Mid-teens mA tubes for those plate volts puts dissipation in the low 20's. Of course less dissipation means tubes should last much longer up to some point of running way too cold.
For 7581A that same 450V translates to 35mA for 45%.
Has anyone here used 7027A's in a coli? If so, what brand?
D
dr teeth
Active member
Maybe the 7027A wouldn't work without some modification. My little understanding is the screen (pin 4) is combined with pin 1 (no pin 1 on 6L6GC tube) and grid (pin 5) is combined with pin 6 (no pin 6 on 6L6GC tube). If the sockets are double pinned for screen and grid as intended the 7027A has improved cooling allowing better plate volts, not that it is needed with this tube for 6L6GC circuits from what I can tell.
I compared the power section of K17x with a blue stripe DRG since both were handy.
K17x has the following for socket wiring: pin 1 tied to pin 3 (plate) and pin 6 tied to pin 7 on hard rails (pin 2 to pin 7 is the heater). The fact that they are on rails makes me think it was done for stabilizing support of the sockets with no electrical consequence since those pins don't exist on the 6L6GC tube.
The blue stripe has pin 1 tied to the cathode (pin 8) via the leg of a resistor that goes to the grid. The connection for pin 6 is snipped on all 4 sockets.
My conclusions:
The DRG/HRG/etc would be very easy to clip apart pin 1 from pin 8 and your mod is done before you got started. Not sure why mesa bothered to span that resistor leg from the cathode to a pin that doesn't exist on the tube. There are plenty of glass options for 450 plate volts.
Tho I've never had a 105 I understand they are 500+V. With the current availability of high plate V tubes this is a very easy solution if you can grab some NOS GE's, RCA's, Sylvania's, or ???. I see TAD makes them. The rub on the IIC+ is that while an easy cooler running solution the tube is big in the hi-fi world and the clarity may be the opposite tonal structure desired for some while Prince may have loved it with the right pedals, who knows. Yet I don't see too many people bad mouthing the 415 for high gain in the IIC+. To me preamp tubes are better suited for gain structure.
With the coli railing up the sockets for structural support tho it would mean adding 2 rails to make 4 where there are currently 2 rails. The upside with that mod would be the extra cooling if you ran 7027A and the downside is you had to break out the soldering station and buy a couple rails.
Makes me wonder if over all these years the factory has modded one for the 7027A. It's not a new tube. There is not a shumacher provided to mesa that the 7027A couldn't handle calmly given it's plate volts handling and 35 watts. The only thing that gives me pause and I'm not sure the 7027A numbers follow the same designation but usually the first number of a tube (6V6, 12 AX7) is the tube volts. Many people seem to think it's a juiced up 6L6GC but I don't see if it is a 6 or 7 volt tube.
Godzilla, I hope Western E brings back the Sylvania 7581A.
I compared the power section of K17x with a blue stripe DRG since both were handy.
K17x has the following for socket wiring: pin 1 tied to pin 3 (plate) and pin 6 tied to pin 7 on hard rails (pin 2 to pin 7 is the heater). The fact that they are on rails makes me think it was done for stabilizing support of the sockets with no electrical consequence since those pins don't exist on the 6L6GC tube.
The blue stripe has pin 1 tied to the cathode (pin 8) via the leg of a resistor that goes to the grid. The connection for pin 6 is snipped on all 4 sockets.
My conclusions:
The DRG/HRG/etc would be very easy to clip apart pin 1 from pin 8 and your mod is done before you got started. Not sure why mesa bothered to span that resistor leg from the cathode to a pin that doesn't exist on the tube. There are plenty of glass options for 450 plate volts.
Tho I've never had a 105 I understand they are 500+V. With the current availability of high plate V tubes this is a very easy solution if you can grab some NOS GE's, RCA's, Sylvania's, or ???. I see TAD makes them. The rub on the IIC+ is that while an easy cooler running solution the tube is big in the hi-fi world and the clarity may be the opposite tonal structure desired for some while Prince may have loved it with the right pedals, who knows. Yet I don't see too many people bad mouthing the 415 for high gain in the IIC+. To me preamp tubes are better suited for gain structure.
With the coli railing up the sockets for structural support tho it would mean adding 2 rails to make 4 where there are currently 2 rails. The upside with that mod would be the extra cooling if you ran 7027A and the downside is you had to break out the soldering station and buy a couple rails.
Makes me wonder if over all these years the factory has modded one for the 7027A. It's not a new tube. There is not a shumacher provided to mesa that the 7027A couldn't handle calmly given it's plate volts handling and 35 watts. The only thing that gives me pause and I'm not sure the 7027A numbers follow the same designation but usually the first number of a tube (6V6, 12 AX7) is the tube volts. Many people seem to think it's a juiced up 6L6GC but I don't see if it is a 6 or 7 volt tube.
Godzilla, I hope Western E brings back the Sylvania 7581A.
D
dr teeth
Active member
I had to pull a short chassis B and this is my only short so here is the Mark that constitutes me poking my head in the mark rabbit hole. I thought I left bread crumbs to find my way out but there must be a mesa mouse following me around.
For a 1981 amp (sp 9a) there are 220pF's with a 7 year on them and 30pF's with a 9 year on them. Both are Mesa labelled BMI caps which I don't think I've seen before so I'm not sure what decade these are from. Prob either a 1999 or 2009 loop mod, I'd lean towards 2009 since I doubt they were replacing the filters in 1999 unless one was bad.
For a 1981 amp (sp 9a) there are 220pF's with a 7 year on them and 30pF's with a 9 year on them. Both are Mesa labelled BMI caps which I don't think I've seen before so I'm not sure what decade these are from. Prob either a 1999 or 2009 loop mod, I'd lean towards 2009 since I doubt they were replacing the filters in 1999 unless one was bad.
Attachments
GJgo
Well-known member
Was that the Super60 you brought over to my house a few years ago? That was my first time playing a 60, and I immediately knew the 60s have something going on that the bigger power sections can't do.
D
dr teeth
Active member
That is the same amp.
With all the DRG's and coli's we had going that day it must have made an impression for you to remember this modest monster. And fwiw I still say you should try the DC5 if you get a chance.
Mitch, did you check those tubes yet? I think I forgot to answer where you can find what pre-amp you have. It's right here:
With all the DRG's and coli's we had going that day it must have made an impression for you to remember this modest monster. And fwiw I still say you should try the DC5 if you get a chance.
Mitch, did you check those tubes yet? I think I forgot to answer where you can find what pre-amp you have. It's right here:
Attachments
D
dr teeth
Active member
The newer caps might have "tightened" it up
GJgo
Well-known member
That was the moment I also realized that the IIB was wildly undervalued in the marketplace.
D
dr teeth
Active member
That's been changing even with these loose, wimpy, temperamental, no balls boat anchors.
In an age where the IIC+ rips into 5 figures it's all relative but the little brother seems to be coming into age. It only took about 42.0 years. Unless you count the opinion of Brad Whitford, Keith Richards, Tony Iommi, Prince (until mb retrofitted him), and countless others. But the word forum meant something different back then.
And speaking of which you speak and thank you Markedman, that nj coli was way too cheap imnho.
I owe you a beer too now.
In an age where the IIC+ rips into 5 figures it's all relative but the little brother seems to be coming into age. It only took about 42.0 years. Unless you count the opinion of Brad Whitford, Keith Richards, Tony Iommi, Prince (until mb retrofitted him), and countless others. But the word forum meant something different back then.
And speaking of which you speak and thank you Markedman, that nj coli was way too cheap imnho.
I owe you a beer too now.
IIBornotIIB
Well-known member
The term “musical sledgehammer” comes to mind…. IIB or not IIB, that is the question.
D
dr teeth
Active member
Sledgehammer- yes.
Watching IIC+ prices go up is like watching the fuel guage go down driving with a 4 barrel 460. The latest S I saw stayed on the market a while ($5500?) but I no longer see it.
Now there's a Cincinnati local pickup SX one over 6k. New filters but the blue bling doesn't look like mesa label to me. I'll bet this month they get it even with local pickup. Who knows what they're worth next month.
https://reverb.com/item/53692189-mesa-boogie-mark-ii-c-sx-2-channel-60-watt-guitar-amp-head
That aurora IIB Meeotch grabbed had a couple JAN Phillips pre's in it on top of the flying saucer getter power tubes. What a score! It is RP-9C.
Aurora has been a hotbed of DRG lately with a blonde combo III blue for 2k going quick on cl. It was one of those "simulcast" models you see advertised more often than you would think could be wead wong.
Watching IIC+ prices go up is like watching the fuel guage go down driving with a 4 barrel 460. The latest S I saw stayed on the market a while ($5500?) but I no longer see it.
Now there's a Cincinnati local pickup SX one over 6k. New filters but the blue bling doesn't look like mesa label to me. I'll bet this month they get it even with local pickup. Who knows what they're worth next month.
https://reverb.com/item/53692189-mesa-boogie-mark-ii-c-sx-2-channel-60-watt-guitar-amp-head
That aurora IIB Meeotch grabbed had a couple JAN Phillips pre's in it on top of the flying saucer getter power tubes. What a score! It is RP-9C.
Aurora has been a hotbed of DRG lately with a blonde combo III blue for 2k going quick on cl. It was one of those "simulcast" models you see advertised more often than you would think could be wead wong.
D
dr teeth
Active member
K123
No date but predates my 58X coli which has SP 8C while K123 has SP 8B- I have not seen this pre board before
With K110 being 4/14/81 and K17x at 8/26/81 it's roughly 16 K's per month in between making this a '81 Taurus. The bull!!!
This means my 58x coli was a regular production K that someone either stamped as regular long chassis or grabbed the wrong plate. I like to think humboldt purple kush had something to do with the snafu.
Looks like 2008 service based on BMI mesa label caps. I noticed my 2019 mesa filters are also BMI. The only things I see it could use is a new power cord and one of the front pots is missing the chrome dimple which I'm sure is unobtainable. Anyone got any spare B knobs?
Gander at the 5w ceramic screen resistors instead of 2w carbon comp I'm used to seeing.
No date but predates my 58X coli which has SP 8C while K123 has SP 8B- I have not seen this pre board before
With K110 being 4/14/81 and K17x at 8/26/81 it's roughly 16 K's per month in between making this a '81 Taurus. The bull!!!
This means my 58x coli was a regular production K that someone either stamped as regular long chassis or grabbed the wrong plate. I like to think humboldt purple kush had something to do with the snafu.
Looks like 2008 service based on BMI mesa label caps. I noticed my 2019 mesa filters are also BMI. The only things I see it could use is a new power cord and one of the front pots is missing the chrome dimple which I'm sure is unobtainable. Anyone got any spare B knobs?
Gander at the 5w ceramic screen resistors instead of 2w carbon comp I'm used to seeing.
Attachments
D
dr teeth
Active member
Meeotch
Well-known member
Update: like dr teeth mentioned, I bought the IIB from Music Go Round mentioned earlier. I literally picked it up on my way to a remote work site and finally had a chance to pull the chassis. It's an RP-9C board with 100 OT/PT. HRG 100/60w. Power tubes are winged C's and the preamp tubes are a mix of Sovtek 7025 and JAN Phillips 12AT7's. So rad! I'll plan on sending it in to Mike B eventually but want to live with it a bit to get a good feel for it. The cleans are insane and the lead channel seems promising. Gotta run my quiver of boosts through it and into my full stack when I get home next week to really appreciate it. Here's some pics...huge thanks to dr teeth and all of you for your input. Feeling pretty lucky to have scored this one!
IIBornotIIB
Well-known member
@Meeotch - nice score! Looks to be in really good shape, too! Definitely live with a while to figure out what you do and don’t dig about it. The IIB cleans in the 60/100W are pretty special, IMO. There’s plenty of gain on tap in lead, too. While not as tight as later Marks, it can be improved with proper EQ and boosts. Then there’s always the loop mod, which increases gain, tightness and improves loop functionality - with marginal loss of the really “clean” cleans. Good idea to get it to Mesa for service (and if you think you want the loop mod, presuming Mike B returns to modding later this summer) - caps should be replaced and probably some pots rebuilt. Enjoy it!
R
Racerxrated
Well-known member
I would add this….my late 2B Coli with the RP9C board was tight no boost needed, and the gain was like a 2C/C+. I never did try the loop but it’s probably the first version that needs upgrading.
Congrats on the amp!
IIBornotIIB
Well-known member
Agreed about the IIB KRG... my late Limit Circuit version is comparable in tightness and gain to most C+'s I've owned, more raw (less compressed) and evenly voiced as compared to C+'s. It passes the loop test, without any modifications which is unusual for a IIB. The KRG is definitely tighter than any un-modded B that I have had. The massive iron, available headroom and the fact that this was a transitional B>C version probably all contributes to how crushing the amp is. As I think I've mentioned earlier - I had a RP9A HRG that I did have Mike B loop mod. The mod completely improved the circuit and that amp, too, became a real fire-breather - very close to C+/++ land, but again with that rawness and more even voice.I would add this….my late 2B Coli with the RP9C board was tight no boost needed, and the gain was like a 2C/C+. I never did try the loop but it’s probably the first version that needs upgrading.
Congrats on the amp!
GJgo
Well-known member
Nice score!! That spec with the loop mod will run with a IIC+. The 100 is a great PT. Also remember, it needs a good sealed 4x12 to really show what the lead channel can do... It should kill with any good Mesa Recto or Marshall 1960 cab.
D
dr teeth
Active member
It would seem there are some observant coli watchers here that go back many years. I'm having serious doubts the pre-K100's exist.
We are talking face plates and Mesa so random one-offs have to be expected like a 14350B serial on a IIB+ or the early K Racer had.
The sampling size of what I've made note of is too small to be science but in 3 1/2 months from Oct 81 - Jan 82 there was only an increase of 7 long chassis'. That's 2 per month.
While the power board 30uF's were changed out on my 58x the 8 bank of 220uF's are the original silver 8047 dated which puts the amp around the turn of 1981. If I use that date there was about 3.7 per month for the 1st 9 months of 81 and 6.8 from August 80 to the new year if the 550 starting point can be marginally trusted. If 58x was born in March or so of 81 that smooths out the averages. The average long chassis over the 1st 18 months of IIB was 4 1/4 a month using 550 as the start.
There was about 50 K's in the last 4 months of '81, 12.5 per month. The 4 months before that it was 16 K's per month starting with K110 in April 81. The coli's were more popular than the standard LC.
What throws me is K110 (KRG) has 4/14/81 dates on it, K123 is SP 8B while 58x is SP 8C suggesting the 58x was May-June 81 at the earliest. So maybe pre-K100 exist in numbers but got swallowed up in earthquakes, tidal waves and alien abductions. It makes me wonder though when Mesa 1st started advertising the coli in print and price lists.
Anyone with a early dated coli chassis please chime in with K#, pre amp pcb, and if any original Mallory filters are in there the date, e.g. 8034H..... is 34th week of 1980.
All my IIB coli's I believe have:
P-180321 EIA606-809 and
O180322 EIA606-806
I've always assumed that to be dates 809 and 806 year and month. Are those not the dates? Idr if I've seen any tranny's with 4 numbers after the 606 Schumacher code. This could be a more standard 8 for 1978 and 06 for 6th week which seems highly unlikely being a couple years too early. Unless schumacher made them in 1978, not for mesa particularly and making custom mesa stamped covers later. Doubt it.
If the batch of coli PT's weren't made until the 9th month of 1980 that would bookend the coli's birth. Was it a SP/RP 8A in the 1st one?
Thinking out loud.
We are talking face plates and Mesa so random one-offs have to be expected like a 14350B serial on a IIB+ or the early K Racer had.
The sampling size of what I've made note of is too small to be science but in 3 1/2 months from Oct 81 - Jan 82 there was only an increase of 7 long chassis'. That's 2 per month.
While the power board 30uF's were changed out on my 58x the 8 bank of 220uF's are the original silver 8047 dated which puts the amp around the turn of 1981. If I use that date there was about 3.7 per month for the 1st 9 months of 81 and 6.8 from August 80 to the new year if the 550 starting point can be marginally trusted. If 58x was born in March or so of 81 that smooths out the averages. The average long chassis over the 1st 18 months of IIB was 4 1/4 a month using 550 as the start.
There was about 50 K's in the last 4 months of '81, 12.5 per month. The 4 months before that it was 16 K's per month starting with K110 in April 81. The coli's were more popular than the standard LC.
What throws me is K110 (KRG) has 4/14/81 dates on it, K123 is SP 8B while 58x is SP 8C suggesting the 58x was May-June 81 at the earliest. So maybe pre-K100 exist in numbers but got swallowed up in earthquakes, tidal waves and alien abductions. It makes me wonder though when Mesa 1st started advertising the coli in print and price lists.
Anyone with a early dated coli chassis please chime in with K#, pre amp pcb, and if any original Mallory filters are in there the date, e.g. 8034H..... is 34th week of 1980.
All my IIB coli's I believe have:
P-180321 EIA606-809 and
O180322 EIA606-806
I've always assumed that to be dates 809 and 806 year and month. Are those not the dates? Idr if I've seen any tranny's with 4 numbers after the 606 Schumacher code. This could be a more standard 8 for 1978 and 06 for 6th week which seems highly unlikely being a couple years too early. Unless schumacher made them in 1978, not for mesa particularly and making custom mesa stamped covers later. Doubt it.
If the batch of coli PT's weren't made until the 9th month of 1980 that would bookend the coli's birth. Was it a SP/RP 8A in the 1st one?
Thinking out loud.
Last edited:
D
dr teeth
Active member
And Mitch, blast that bitch thru the full stack and step into the wind tunnel!
It was originally paired with the halfbacks:
4JB EV wl MC90 up CEL/EV 360W
4YB V30 wl MC90 up CEL/VNTG (this being a later version of course)
and the various combinations including VS-12 and MS-12.
Anyone got the more obscure halfback model designations? Was one of them 4HB?
It was originally paired with the halfbacks:
4JB EV wl MC90 up CEL/EV 360W
4YB V30 wl MC90 up CEL/VNTG (this being a later version of course)
and the various combinations including VS-12 and MS-12.
Anyone got the more obscure halfback model designations? Was one of them 4HB?