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August 07, 2020, 05:13:09 AM

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Author Topic: Barcus Berry 1720 Power Transistors  (Read 2774 times)

Micajah

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Barcus Berry 1720 Power Transistors
« on: July 06, 2020, 07:37:59 PM »
I’m working on a 1977 Barcus-Berry 1720 / 2X10 Combo Guitar Amp - seems to be specific to acoustic instruments.
I tend to focus on Tube amps but have successfully restored SS amps in the past. This one has me stymied.
The output transistors are blown - I checked them with my Peak Atlas DCA55. One shows "no component attached" - the other one a short between the case and one of the pins.
I have the schematics but in true Bob Crooks’ design (of Standel secret circuit fame) the output transistors are labeled with a Barcus Berry Part number - both on the schematic and the physical transistor case. No other physical marking other than 630 032 and 630 033.
I've searched a lot online and come up with zero results.
Sent emails to BBE and there response: All the Barcus Berry schematics were given to MBT international which is the owner of that company. We do not have any of the wiring diagrams or parts, All the best."
MBT or KMC Music which were the last companies connected to these amps have not responded.
Does anyone on the forum have any insight? or Is it possible to reverse engineer what transistor these are based on the schematic? I've attached a link to the schematic.
Thanks ahead of time for any info.

nosaj

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Re: Barcus Berry 1720 Power Transistors
« Reply #1 on: July 06, 2020, 08:30:45 PM »
no link to schematic

nosaj

Micajah

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nosaj

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Re: Barcus Berry 1720 Power Transistors
« Reply #3 on: July 07, 2020, 08:39:07 PM »
Over on the antiques radio site this is what mikemco said and he's been very helpful in the past

If they're TO-3 devices I'd use a 2N3055 and Mot MJ2955 devices. That's a pretty old design.
Here's the link I posted in asking about them.
https://antiqueradios.com/forums/viewtopic.php?f=19&t=380491&p=3228414#p3228414

nosaj

Micajah

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Re: Barcus Berry 1720 Power Transistors
« Reply #4 on: July 07, 2020, 08:44:20 PM »
Thanks man - above and beyond! I'll give them a try and let you know what happens.
Micajah

nosaj

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Re: Barcus Berry 1720 Power Transistors
« Reply #5 on: July 07, 2020, 09:10:04 PM »
That's what we do. i just happen to have the ability to google my peers instead of the web for info. But bet your life this info will disappear as the older generations pass on. 

nosaj

tonyharker

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Re: Barcus Berry 1720 Power Transistors
« Reply #6 on: July 08, 2020, 06:07:12 AM »
Looking at the drive current through Q4 only 8mA approx, I would suggest that the output transistors are Darlington transistors, in which case 3055/2955s wouldn't be suitable. If they are TO3 cases try MJ11015 pnp and MJ11016 npn as replacements if you can get them.  If they are plastic types then TIP142 and TIP147 would work.

nosaj

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Re: Barcus Berry 1720 Power Transistors
« Reply #7 on: July 08, 2020, 07:15:24 PM »
Thanks man - above and beyond! I'll give them a try and let you know what happens.
Micajah
Others have chimed in on the antiques radio site.
You need to follow the discussion and maybe join in https://www.antiqueradios.com/forums/viewtopic.php?f=19&t=380491&sid=69024ce61d0ae3bd883d4ecc43947adf&p=3228889#p3228889
nosaj