'69 100w Super Lead between SL/A10500 thru SL/A10800 ?

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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Tue Sep 08, 2015 1:58 pm

LD50 wrote:The interesting thing I would like to know is when the change from 820R to 2k7 occurred?


Yeah, I wish we could narrow that down a little. I believe 'appetite4distortion' mentioned having a Super Lead with an September of '69 date that had a 2K7. I've seen a Super Lead SL/A23xxA (August 11th 1969) that had the 820R resistor. So far it looks like sometime in September Marshall may have started phasing in the 2K7 resistor.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Ned B on Tue Sep 08, 2015 3:02 pm

I had a 09/69 with the 2.7K and I have a 02/70 with the 820. I find the latter more explosive sounding and the 2.7K a "safer" sound. When I got the '70 it had a 10K V2 bias resistor as factory original which I figured was a mistake as mistakes aren't that rare, but now I wonder if they were taming it down on purpose.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Tue Sep 08, 2015 4:37 pm

Ned B wrote:I had a 09/69 with the 2.7K and I have a 02/70 with the 820. I find the latter more explosive sounding and the 2.7K a "safer" sound. When I got the '70 it had a 10K V2 bias resistor as factory original which I figured was a mistake as mistakes aren't that rare, but now I wonder if they were taming it down on purpose.


Glad you chimed in Ned....I know you've had a lot of Marshall's run through your stable. So, it looks rather convincing that the 2K7 started to show up in September of '69. It also appears that it was more of a phasing in rather than an absolute change.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby coony on Fri Sep 11, 2015 9:38 am

Hello,

Anyone took some voltage measurements from their '69 super lead and would care to share them? Maybe a voltage chart?
This would be usefull to check my '69 plexi (serial SL/A 106xx)!

Thanks!
play 'em loud !
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Fri Sep 11, 2015 2:14 pm

coony wrote:Hello,

Anyone took some voltage measurements from their '69 super lead and would care to share them? Maybe a voltage chart?
This would be usefull to check my '69 plexi (serial SL/A 106xx)!

Thanks!


From what I've seen the B+ voltage tends to be around 490vdc through 500vdc on pin #3 of the output valves. The only "official" Marshall voltage chart that comes to mind as being somewhat close for the '69 Super Lead might be the one found on the model 2003 (P.A.) schematic.
You should post pictures of your amp SL/A106xx since I'm sure some of us here would love to see it.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby LD50 on Fri Sep 11, 2015 2:32 pm

With a T 2562PT I see 490v on UK voltages pretty consistently.
All bleeding stops.......eventually.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby LD50 on Fri Sep 11, 2015 2:32 pm

With a T 2562PT I see 490v on UK voltages pretty consistently.
All bleeding stops.......eventually.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby coony on Sun Sep 13, 2015 8:51 am

I'll try to take some pictures!

What about preamp voltages? A schematic with recorded voltages would be great!

Best regards
Koen
play 'em loud !
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Mon Sep 14, 2015 2:55 pm

Here's a voltage chart I quickly whipped up. Also, there's a voltage chart in the MetroAmp 100w plexi amp kit pdf that should also be very close for the '69 Super Lead.

Image
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Jimmy82 on Wed Sep 16, 2015 3:53 pm

Measuring the voltages in vintage amplifiers, you have to take in consideration that line voltage (in USA) is not 110v like in 1970s.
If I am right it is 117v. So if your voltage selector is on 110v, B+ will be at least 7Vac * 3.18 * 1.41 = 31.5Vdc higher than it had to be in 1970s.

Number 3.18 is out of secondary/primary winding ratio 350v/110v.

I think that B+ 460v instead of 490v will make a difference.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Wed Sep 16, 2015 6:36 pm

Actually, in 1970 AC voltage in the USA was between 115Vac through 120Vac depending upon where you lived in the country. In the northeast the voltage was 120Vac, and was considered 'Type 3' when it came to design specifications. By 1968 Marshall were using Dagnall transformers (T2562) that were designed with a '120Vac' input tap. Now, whether Dagnall used 115, 117, or 120Vac as there design parameter for there '120Vac' input tap; I don't know for sure.
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Third Best Friend on Sun Sep 27, 2015 8:00 am

Hi everyone,

This is my first post on the forum having just joined. Last week I was fortunate to locate and purchase this 1969 JMP 100 watt plexi head and matching cabinet. The amp's serial number is 10777 so it falls right on topic with this thread! I'm the third owner since new and as far as I am aware there's been no modifications other than the power socket for Aussie power. The amp was formerly owned by the guitarist from early Aussie prog rock group Madder Lake and it appeared on a number of the band's albums.

Image

http://s210.photobucket.com/user/rick_o ... ort=3&o=12
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby coony on Tue Oct 06, 2015 1:16 pm

Tazin wrote:Here's a voltage chart I quickly whipped up. Also, there's a voltage chart in the MetroAmp 100w plexi amp kit pdf that should also be very close for the '69 Super Lead.

Image


I finally got some time to check the voltages in my plexi, they're very close to yours Tazin, except for the grid voltages at pin 2 of V3; mine are at about 27V each (which is identical to the voltage chart you mentioned of the MetroAmp kit) while yours are quite a bit lower?

Furthermore, at what bias current were you taking those measurements? Mine is set at -43,3V with a current of about 26~28 mA per EL34 tube. Maybe a bit on the cold side, but at full power, the amps starts getting very hot after 2 hours of playing!

Some more observations:
*with an incoming voltage of 230V and the voltage selector set at 220-230V, the heater voltage was at about 6,6V AC, quite high
*with the same incoming voltage but the selector set at 240V, heater voltage was at about 6V, so I took my measurements at that setting.

Thanks for sharing!
play 'em loud !
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Tue Oct 06, 2015 2:49 pm

That voltage chart is from about five years ago. As to why the grid voltage at pin #2 of V3 was low; I don't know for sure but it may have to do with how the tone controls are set when the voltages are taken. The voltages were taken after I biased up the amp. I use the 1 ohm resistor cathode method and shoot for 17 watts of dissapation at idle. I use a dummy load (either a 16 ohm 300w resistor or a Hotplate set to 'Load') when I bias amps. In addition, I set the tone controls either to 0 or sometimes to 10, but the volume(s) are always at 0. On the original voltage chart I have 34ma written down as the current draw per output valve.....And that works out to 17 watts per valve when you do the math.
No pictures yet?
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Re: '69 100w Super Lead between SL/A10500 thru SL/A10800 ?

Postby Tazin on Tue Oct 06, 2015 2:53 pm

Third Best Friend wrote:Hi everyone,

This is my first post on the forum having just joined. Last week I was fortunate to locate and purchase this 1969 JMP 100 watt plexi head and matching cabinet. The amp's serial number is 10777 so it falls right on topic with this thread! I'm the third owner since new and as far as I am aware there's been no modifications other than the power socket for Aussie power. The amp was formerly owned by the guitarist from early Aussie prog rock group Madder Lake and it appeared on a number of the band's albums.

Image

http://s210.photobucket.com/user/rick_o ... ort=3&o=12



Looks like she's seen a lot of use. If you ever get a chance you should snap some pictures of the electronics and post them here we'll let you know of any changes to the circuitry. BTW, how does the amp sound?
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