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Old 21st Mar 2014, 1:59 pm   #1
Tubeglow
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Default Transistor types in Bi-Pak AL60 modules?

I am trying to find the transistor numbers on the AL60 module.

Could anyone tell me the numbers of the small transistors and the one in the middle of the heat sink.

A list would be useful going from bottom left (component side) across the board.

Also the transistor on the middle of the heat sink.
I used TIP 41A for the power transistors in the past..however I have lost all the info I had.

Its a nostalgia trip...I made two stereo amps many years ago using theses modules and I found a photo of the track side of the board.
So I am thinking of making a couple just for fun..

Here are the pics.

Thanks for any help.

Regards, Tubeglow.
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Last edited by Station X; 22nd Mar 2014 at 10:07 am. Reason: Threads merged.
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Old 21st Mar 2014, 11:58 pm   #2
Biggles
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Default Re: Transistor types in Bi-Pak AL60 modules?

I'll have a look on mine and see if I can see any numbers on them and let you know.
Alan
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Old 22nd Mar 2014, 12:31 am   #3
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Default Re: Transistor types in Bi-Pak AL60 modules?

Thanks,

Could you list them from bottom left to right up to top heatsink

The identity of one in the middle of the heat sink would be useful as well.

Tubeglow.

Last edited by Station X; 22nd Mar 2014 at 10:08 am. Reason: Threads merged.
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Old 22nd Mar 2014, 10:30 am   #4
vidjoman
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Default Re: Transistor types in Bi-Pak AL60 modules?

They are Ferranti E line transistors normally with a ZTX number. There are numbers visible on the photo but I can't read them.
Quad used them for a time in the 303 power amp.
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Old 22nd Mar 2014, 10:35 am   #5
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Default Re: Transistor types in Bi-Pak AL60 modules?

Quote:
Originally Posted by vidjoman View Post
Quad used them for a time in the 303 power amp.
I didn't know that..thanks..
Yes it would be nice to know the numbers..I was going to try and draw out the circuit..there doesn't seem to be any info on the web..
Unless anyone wants to have a go<<easier with one in your hand..LOL

Tubeglow.
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Old 22nd Mar 2014, 10:39 am   #6
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Default Re: Transistor types in Bi-Pak AL60 modules?

Since Bi-Pak dealt in surplus devices, the transistors used might vary, and may not be full spec.
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Old 22nd Mar 2014, 10:52 am   #7
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Default Re: Transistor types in Bi-Pak AL60 modules?

ZTX-prefix transistors are still being made. Ferranti's transistor/diode arm became Zetex and has since been bought out by Diodes Inc. Their devices were surprisingly capable, high current capability and high gain in small packages.

Though I think all current produce are SMT

Bi-pre-pak bought spec failure parts and their cases had odd markings if any at all. To replace a device you need to trace out the circuitry and reverse engineer it enough to decide what device ratings are needed.

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Old 22nd Mar 2014, 11:47 am   #8
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Default Re: Transistor types in Bi-Pak AL60 modules?

Bi-pak and Bi-pre-pak were seperate companies, no connection betweeen them that I know of. Very confusing really...

It's quite likely all the same, that the Bi-pak modules used 'below-par' transistors. That being so, looking at the circuit and using a bit of inspiration to select suitable full-spec devices, should give a very good chance of success.

The circuit could have been conservatively designed, to use transistors which showed more leakage than the spec they were manufactured to meet. Alternatively, Bi-pak may have bought transistors which didn't meet their switching speeds, frequency spec, breakdown voltage, etc to be labelled and sold as full-spec devices.

Whatever, if you use transistors with a Vceo rating of the full rail-rail supply voltage, you'll be OK. The output devices should have a current rating at least equal to supply voltage divided by loudspeaker impedance (and good design would double this). And the remaining transistors should have a current rating as determined by circuit resistances etc - if in doubt use 500mA rated types for small signal positions with a gain of at least 100. Finally, the pinout must of course suit the PCB layout.

Luckily, bipolar transistors are all much of a muchness otherwise - we don't have to worry about turn-on threshold, mutual conductance, etc as they are all the same! Only other parameter which varies is forward current gain, but as long as that is high, it doesn't usually matter.
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Old 22nd Mar 2014, 1:26 pm   #9
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Default Re: Transistor types in Bi-Pak AL60 modules?

Quote:
Originally Posted by Radio Wrangler View Post
ZTX-prefix transistors are still being made. Ferranti's transistor/diode arm became Zetex and has since been bought out by Diodes Inc. Their devices were surprisingly capable, high current capability and high gain in small packages.
Well,

I'm hoping Biggles can read them..
Its a shame there isn't a circuit diagram on the web.

Tubeglow.
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Old 22nd Mar 2014, 8:44 pm   #10
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Default Re: Transistor types in Bi-Pak AL60 modules?

Right, I have had a look and found that not all are marked with a type number. Nothing, not even a house number, which would confirm suspicions that they may have been surplus items. Anyway, the ones that are marked are as follows. Starting from bottom left, with the heatsink at the top and looking at the component side of the PCB.

First bottom left PNP type no markings (looks like a ZTX)
immediately to the right of that one, NPN no markings (looks like a ZTX)
To the far right of that, another unmarked NPN ZTX type
To the top left, immediately under the left power transistor, BFS61
To the top right immediately under the right power transistor, BFS98
The power transistors on the heatsink are both 2N6122
The temp sens transistor in between the power trannies is a TO92 type BC171A
Hope that helps. If you do work out a circuit I wouldn't mind a copy so I can build another one as no one seems to have any of these modules in the junk box. There must have been thousands sold in the late seventies.
Alan.
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Old 22nd Mar 2014, 9:40 pm   #11
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Default Re: Transistor types in Bi-Pak AL60 modules?

This is what we have so far?

Is this correct?
Thank's for the information..

The 2N6122 can be TIP41A..I'm sure that's what I used in the past..
First transistor from the input is PNP? via electrolytic capacitor? (22uF)

Any markings on the ceramic caps?

Tubeglow.
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Old 23rd Mar 2014, 1:51 am   #12
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Default Re: Transistor types in Bi-Pak AL60 modules?

The small disc ceramic across the input (at the bottom right of the board is marked 470M (470pF?)
The small disc ceramic between the RHS power transistor and the temp sens is 3900 (3.9nF)
The large square ceramic just above the first PNP to the left bottom of the board is marked M47 (470nF?) and the small square ceramic towards the mid right of the board is marked 22p (22pF). The first transistor (input) after the 22micro cap is a PNP. I was thinking this is strange but the cap is polarised correctly for that and the amp uses a split supply so it will be right. The poly cap under the temp sens transistor is 47nF.
Alan.
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Old 23rd Mar 2014, 2:41 am   #13
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Default Re: Transistor types in Bi-Pak AL60 modules?

This is a first attempt.

IT'S NOT CORRECT

Thought you might be able to have a look at the values on the board.
Its hard to see some of the the colours ..
Its just an initial drawing for a starting point..done over a couple of hours.
I will take a closer look perhaps tomorrow.
Some of the values and output connections don't make sense at the moment.
I flipped the track side and compared to the component layout.
The transistor above the BFS98 is the sense transistor (middle heat sink)

Tubeglow.
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Old 23rd Mar 2014, 9:24 am   #14
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Default Re: Transistor types in Bi-Pak AL60 modules?

So for those interested..

Flipped track with component side.(looking through the board)
I'll try tracing it out against the diagram to eliminate errors.
Its quite interesting to see what I was using way back..
Also it will be interesting to see what it looks like for real because this is strange..so it must be errors.
I just drew what I saw (perhaps think I saw)..LOL

Tubeglow.
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Old 23rd Mar 2014, 9:32 am   #15
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Default Re: Transistor types in Bi-Pak AL60 modules?

Don't forget the external output capacitor. The output will have DC on it at about half the rail voltage.
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Old 23rd Mar 2014, 9:38 am   #16
Tubeglow
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Default Re: Transistor types in Bi-Pak AL60 modules?

Yes on the back of the box (photo)post #11..it is 470uF to speaker and return to Gnd.
Single supply. Lots to sort out yet..to many anomalies..
The first transistor picking supply up from the OP rail doesn't make sense to me?? (Must be wrong)
Just looked again looks the same??

Tubeglow.

Last edited by Tubeglow; 23rd Mar 2014 at 9:55 am.
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Old 23rd Mar 2014, 10:26 am   #17
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Default Re: Transistor types in Bi-Pak AL60 modules?

The smaller transistors look to be in plastic package shapes used by Ferranti, so those are going to be ZTX prefix types.

Around that time the semiconductor firms were producing applications stuff on how to do silicon transistor audio stuff. I have the Mullard little blue book here, but Texas did a larger one in a mostly white dust-jacket. One used to be in the library at HP, but I can't remember the title. It had their applications circuits from then the TIP series power transistors came out.

It's often worth having a look through transistor applications data because a lot of equipment designers never strayed far from them.

I suspect the first transistor gets its supply from the decoupling capacitor part way down the resistors biasing its base.

David
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Old 23rd Mar 2014, 10:28 am   #18
Tubeglow
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Default Re: Transistor types in Bi-Pak AL60 modules?

Just noticed,

I think I missed the decoupling cap across the supply rails looks like 22uF 50V.

Slight distraction by the Alien technology..
Quote:
Originally Posted by Biggles View Post
The small disc ceramic across the input (at the bottom right of the board is marked 470M (470pF?)
The small disc ceramic between the RHS power transistor and the temp sens is 3900 (3.9nF)
The large square ceramic just above the first PNP to the left bottom of the board is marked M47 (470nF?) and the small square ceramic towards the mid right of the board is marked 22p (22pF). The first transistor (input) after the 22micro cap is a PNP. I was thinking this is strange but the cap is polarised correctly for that and the amp uses a split supply so it will be right. The poly cap under the temp sens transistor is 47nF.
Alan.
I have added the cap values to the drawing..I'll post it again shortly,

It would be interesting to trace it against the module..see what the errors are compared to the drawing..


Tubeglow.
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Old 23rd Mar 2014, 11:36 am   #19
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Default Re: Transistor types in Bi-Pak AL60 modules?

When I get a few minutes I'll compare your circuit with my module. Although I used mine with an output decoupler, I was wondering if the module was originally designed for split supply working. I think there is a 0V, +V and -V marked on the board but they are hard to make out. I have a link soldered across 0V and -V on mine. I remember a resistor burning out at one time and I had to guess what the value was. Don't remember how it happened, I think I was about 15 at the time.
Alan.
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Old 23rd Mar 2014, 12:01 pm   #20
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Default Re: Transistor types in Bi-Pak AL60 modules?

I once used two AL60s to repace faulty amplifier boards in a Sinclair Project 60, which I still have around somewhere)In this I fitted speaker coupling caps. (1000uf from memory) beacuse I was still using the single rail Sinclair PSU, though I guess that, if a split supply is used, the circuit would work quite happily wired this way. As to diagrams, I traced out the circuit and drew it, but this was years ago. If I can find it I'll post it on here. Oddly, the Sinclair Project 60 booklet include full circuit diagrams of the pre amp, power amp, and PSUs used, but no PCB layouts. Bi-Pak obviously didn't see the need to do likewise!
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