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Old 19th August 2010, 02:56 PM   #1
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Default Rebuilding the Traynor Mono Block II

I have a Traynor Mono Block II bass guitar amp that has a tendancy to fry power transistors. I've talked with several others that have told me that this is a common problem with this model. The transistors are getting more difficult to find and I would like to rebuild the power amp section into something more reliable. The amp is rated to produce 325 Watts at 2 Ohm load and it uses + - 56V rails. I don't care if I end up with an amp that is that powerful but I would like to at least end up in the 150W @ 4ohm range. What power output circuit would you recommend for this rebuild?

I've build many tube amps and a lot of solid state preamps and signal processors but this will be my first solid state power amp.
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Old 20th August 2010, 12:55 AM   #2
Enzo is online now Enzo  United States
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2N5630? That may have been a good choice in 1976, but the common MJ15024 would drop right in its place. DOn't mix, replace the whole group of four.

I am assuming those, since the 2N3773s in the later version are not hard to find.

Running a 4 ohm load, and thus drawing half as much power, would make the amp work a lot less harder than at 2 ohms.

I don't know why they could be prone to blow ups, but the bias circuit is extremely crude - a single dual diode. I am sure it works as well as they intended when everything is fine, but if the junction drop voltages in that part start to climb, then idle current goes up and up.

Once repaired, let the amp sit there powered up and idling. Does the heat sink get hot under those conditions?
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Old 20th August 2010, 03:56 AM   #3
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Yes, I can find 2N3773 but it usually pops the SJ5480 (Q9) also. If I use the 2N3773 can I use it's compliment, the 2N6609 for Q9? What should I use for Q1 and Q9 if I use the MJ15024? Also, what do you suggest for improving the bias circuit?

I never run it down to 2 ohm load, almost always 4 ohm and often only 8 ohm.

Once I get it rebuilt, I'll let it idle a while and see how hot the sinks get.

Thanks for your reply Enzo.
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Old 20th August 2010, 03:24 PM   #4
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you may as well built a more decent VBE multiplier arround this circuit that will provide by far better thermal stability...

mod like the above will need verification with scope and generator to make sure that nothing oscilates from the change of the transitors or the wiring issues that are often a problem with this setups

adding decoupling 100MF/100 volt next to the transistors from rail to ground will also add something to the total performance but it needs to be done carefully

other than the above i like this circuit ....

regards sakis
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Old 20th August 2010, 05:10 PM   #5
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Quote:
Originally Posted by sakis View Post
you may as well built a more decent VBE multiplier arround this circuit that will provide by far better thermal stability...
Can you give me an example for the VBE multiplier?
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Originally Posted by sakis View Post
adding decoupling 100MF/100 volt next to the transistors from rail to ground will also add something to the total performance but it needs to be done carefully
What do you mean by "carefully" with respect to adding the 100MF/100V caps?
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other than the above i like this circuit ....
This amp may be an older design, but it still has a very good reputation among bass guitar players for having a very good tone, response and power. I'm glad a couple of you think it's worth rebuilding instead of gutting and starting over. I'll pop it open and take pictures so you can see how it's laid out.
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Old 20th August 2010, 05:32 PM   #6
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i am not aware how the circuit is builted .... i think its made with cables from pcb to transitor outpouts ...if there decoupling is needed then next to rails and close to transitors you need a ground cable ...tha can cause complications

then again pictures will help

a decent vbe multiplier is made out of a proper tranistor that can easly be a bd 135 a trimer and few resistors ... actually your diodes might work better but have noa adjustement and also i am not really sure that have perfect thermal and mechanical contact with the heatsink.... again some picture might help

another thing that i could try to is to convert the circuit to a coplementary amplifier than a quasi .... easy task but yet again needs to be verified and checked very properly before put to work ...

kind regards sakis
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Old 21st August 2010, 03:48 AM   #7
Enzo is online now Enzo  United States
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The complement of the MJ15024 is the MJ15025.

I am not into redesigning the amp, others can do that. I have no improvement ideas for the bias, Sakis is making a suggestion. My concern is that if the amp is eating transistors, CHECK that dual diode to see if it is slipping.

You should be able to use the MJ15024 exactly as you would the 2N3773. SO if they use 2N3773 for both the outputs and the + side driver, The MJ15024 would work for both applications as well. And the MJ15025 on the V- side.
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Old 21st August 2010, 04:17 AM   #8
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I can get the MJ15024G and MJ15025G from mouser. Might be best just to replace the diodes too. Hopefully the newer transistors will hold up better.
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Old 21st August 2010, 05:36 AM   #9
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They show a 2N3773 as the driver (Q1) in the later amp, is that right is it a TO3 case device?

The bias diodes are fine, it is class B underbiased and if you want to retain the classic design leave that alone.

I'd have to wonder if the CFP side is oscillating and causing the driver failure, if not the failure in the first place. Do both output devices fail when it goes?

If you want to go to a modern device I'd make it an MJ21194G.

Replace all the electrolytic caps due to age.

Check all the diodes. Check R29 if it is bad also replace C11.

Test Q6 and Q7.
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Old 21st August 2010, 07:29 AM   #10
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I can get the MJ15024G and MJ15025G from mouser. Might be best just to replace the diodes too. Hopefully the newer transistors will hold up better.


to my understanding this approach is wrong .... there is no "drop in" replacement transistors any variation an the transitor specs will have grate effect on the bias and total performance

presumambly the double diode will be almost unobtainable so dont bother looking for it ...

to my opinion any change will need to be verified by instruments

and finaly redesign from quasi to complementary will not happen by replacing the lower transistor of course it will take more than that ...

simple as that if you have approach to instruments and procedure go ahead play but verify your work ...if not just replace the broken and any capacitors that might be old and moove on ...

regards sakis
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