28th Nov 2020, 3:37 pm | #41 |
Octode
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Re: Identification of unknown PA amplifier
I'll give you some good photos of the board. At some stage I'll map the circuit out as you know can be a bit time consuming.
Well lucky enough I've just found these transistors exact match and only 2 left of each so be buying those now. |
28th Nov 2020, 5:26 pm | #42 | |
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Re: Identification of unknown PA amplifier
Quote:
Oops- that should be week23, 1982!
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28th Nov 2020, 8:39 pm | #43 |
Octode
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Re: Identification of unknown PA amplifier
I got the code wrong on one they are TIP33C & TIP34C Not sure why 30 was in my head.
Well lucky enough I've managed to source NOS for both and also the little chips think that's what they are. Could not source the power transistors plenty of so called new around but I'd think there copies and bound to be completely different spec to the originals. Could take a chance but have a think on that one. |
28th Nov 2020, 9:03 pm | #44 |
Octode
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Re: Identification of unknown PA amplifier
What is the little 8 pin chip ref no
I have been busy all day working on a minimalist amplifier schematic because of the one you have posted 50 watts plus out of 1 op amp and 4 transistors trev |
28th Nov 2020, 9:36 pm | #45 |
Octode
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Re: Identification of unknown PA amplifier
Your getting quite into that Trev.
Texas 741(uA741CP) |
28th Nov 2020, 9:43 pm | #46 |
Octode
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Re: Identification of unknown PA amplifier
Yep
I thought it would be a 741 back in the day this was the goto op-amp H+H used them a lot as well as other manufacturers Same as in the Texan also ! I have drawn three variants on this them today Not been so keen in a long long time Many thanks Trev |
28th Nov 2020, 9:58 pm | #47 |
Octode
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Re: Identification of unknown PA amplifier
I also managed to get nos bridge rectifiers for it as well. So when all come and fitted it should run like new.
Glad it's spurred up an interest for you again. |
29th Nov 2020, 10:07 am | #48 |
Octode
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Re: Identification of unknown PA amplifier
Well your not gonna get these as genuine parts.
2SB554/2SD424 none have that figure of 8 recess on their bases all flat bumer. |
29th Nov 2020, 10:11 am | #49 |
Octode
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Re: Identification of unknown PA amplifier
Plenty of equivalents out there but beware of the fakes.
Trev |
29th Nov 2020, 10:29 am | #50 |
Octode
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Re: Identification of unknown PA amplifier
Okay Trev any suggestions most welcome.
So are you gonna build these modules? I'll pull boards out today give you resistor ratings etc. Quite a few 1/4 watt in there. I might change these all out ive used AMRG resistors before come in 0.75w and 2 watt bit expensive but reliability and sound reproduction perfect. I've used many resistors from 5p upwards obviouslyif you have a 1930s valve radio your not gonna chuck in quality resistors no point. But if you have a quality bit of kit worth the investment. This amp cost me nothing up until now and I already had some large panasonic psu caps so I'd quite happily spend around 100 quid on it. Oh had to buy XLR connectors I have plenty of rca panel mount sockets but wanted to keep the xlr sockets. Keep going Trev be interesting to see what you come up with. |
29th Nov 2020, 12:25 pm | #51 |
Octode
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Re: Identification of unknown PA amplifier
The first transistors that come to mind are mj15024/mj15025
These are used by lots of high power amplifier manufactures are available at a fair price and are well known to be robust Obtain from a trusted source I use Rs /Farnell Trev |
29th Nov 2020, 1:52 pm | #52 |
Octode
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Re: Identification of unknown PA amplifier
Okay cheers Trev yeah I use those never had a fake yet.
Resistors All on a single board so you would need double the amount. Following 1/4 watt 5% 10k x1 12k x1 22k x1 220k x1 27k x1 2.7k x4 3.3r x2 1.5k x1 10r x1 330r x1 33k x1 4.7k x1 680r 10% 3.4k x2 1 watt 40r x1 2% 27k x2 wirewound 5 watt? 72r x1 wirewound 5 watt? Might both be 7 watt. 22k carbon track preset potentiometer marked E Main electrolytics where 2500uf dual cans 63v x4 The other 2 are 22uf 63v. Hopefully that's of some help. |
29th Nov 2020, 1:57 pm | #53 |
Octode
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Re: Identification of unknown PA amplifier
Looking at those I would assume I'd need the bipolar not the npn?
Cheers Chris |
29th Nov 2020, 2:34 pm | #54 | |
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Re: Identification of unknown PA amplifier
Quote:
Something got lost in translation... NPN and PNP are both bipolar transistors, just opposite polarity types. David
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29th Nov 2020, 2:46 pm | #55 |
Octode
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Re: Identification of unknown PA amplifier
Got it now 2sb554 is a pnp
2sd424 is npn |
29th Nov 2020, 2:47 pm | #56 |
Octode
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Re: Identification of unknown PA amplifier
The 27k x 2 are you sure I suspect 270 ohm x 2
Trev |
29th Nov 2020, 3:01 pm | #57 |
Octode
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Re: Identification of unknown PA amplifier
The green one pic attached read it wrong saw 27k moved round R27K
But I'm getting 0.5r reading? |
29th Nov 2020, 3:07 pm | #58 |
Octode
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Re: Identification of unknown PA amplifier
Are you meaning the wirewound or the 1/4 watt?
Pic of two 1/4 red violet orange 27k. |
29th Nov 2020, 3:13 pm | #59 |
Octode
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Re: Identification of unknown PA amplifier
Looking at my ones the pf collector capacitance rating on mj,s is only 500 whereas on originals 700pf and 900pf so thats 30%/45% difference. Should that be okay?
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29th Nov 2020, 3:34 pm | #60 |
Octode
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Re: Identification of unknown PA amplifier
I'll pull those wirewound out numbers on case not tallying with readings I'm getting one is reading 0.3r but has r27k and other 72r but reading 33r? Could be because in circuit.
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