Re: Transistor types in Bi-Pak AL60 modules?
 

No idea tbh. Its just a classic design from that era... but you'll be amazed how good it can sound.

Re: Transistor types in Bi-Pak AL60 modules?
 

It will be interesting,

to make a hard wired version and try some resistor and capacitor types.

The Output cap is quoted as 1000uF for 4ohm and 470uF for 8 ohm.

The voltage quoted for the amp is different for 4 and 8 ohms.

No wonder the records sounded so good..;D back in 1970's.

What effect did you find with the output cap value?

Tubeglow.

Re: Transistor types in Bi-Pak AL60 modules?
 

I managed to check the values from the PCB today and the circuit is correct, but some component values need updating. With ref to your diagram in post 31;

C11 is 2.2 micro not 22
R2 82K not 8.2K
R3 12K not 1.2K
R10 1K not 10K
R11 820 ohm not 72 ohm
R14 91 ohm not 910 ohm
R15 1K not 1.1K
R16 2.7K not 2K
R19 5.6 ohm not 56K

On my module there is a separate neg supply presumably for split supply working without the output capacitor but I must admit I used mine with a single rail and linked the 0v line to -ve. With ref to your diagram in post 31 basically the -ve supply is connected to TR8 emitter, the bottom end of R14, and the bottom end of R19. Everything else is taken back to the 0v line including the speaker -ve. Hope that helps.
Alan.

Re: Transistor types in Bi-Pak AL60 modules?
 

Hi Mooly,

I've been playing with the amp in Simetrix working from the later sketch circuit and using TIP41A and various likely looking ZTX types for the devices.

I found to start with that the output sat well above mid rail unless I played with the input stage bias resistors and also that the clipping was very asymmetrical, only getting down to about 10V at the output midpoint.

Did you try thrashing it in your sim to see what happened? I'll have another play later tonight using your circuit values and my transistor selection to see what happens then.

Re: Transistor types in Bi-Pak AL60 modules?
 

470uf as an output cap would, by today's, standards be considered way too small. With an 8 ohm load it would give a -3db point of around 42Hz. The 3300uf I used brings that down to nearer 6Hz. You could go bigger still and many would.

The supply voltage is directly linked to the power output available, well actually that's a a term we should get away from it's linked to the maximum voltage swing that's available. For an amp like this, and with suitable transistors, a good supply voltage would be in the 50 to 60 volt range and allow the use of 63 volt caps.

Re: Transistor types in Bi-Pak AL60 modules?
 

OK,

here is what I have at the moment with values from the module.
Curtsy of Biggles.
It would seem the output cap can be much bigger. (to be tested)
It is a bit rushed..:)

0.22 ohm to be added to the output transistors.
Transistors from Mooly01.

Tubeglow.

Re: Transistor types in Bi-Pak AL60 modules?
 

OK, here is the new sim with the updated values. I used some different devices although it doesn't really affect the result.

(if you run this one make sure you put the text file in the same folder as the sim)

Thanks Alan, I've put those into the sim. Using split supplies on an amp like this while do-able wouldn't be recommended these days. The circuit has no pretension to DC stability and the nominally 0 volt output would wander alarmingly due to thermal drift. AC coupled on single rail and its no problem.

Circuits like this have huge potential though, its infinitely tweakable... it depends on what your aims are and how far you would want to push the envelope. Using vertical FET's would be one option, lateral FET's another and that really could make a unique amplifier with huge potential sonically.

Re: Transistor types in Bi-Pak AL60 modules?
 

What was the THD?

C5 is different..is my drawing wrong?

Tubeglow.

Re: Transistor types in Bi-Pak AL60 modules?
 

0.014% but don't get to hung up on the numbers. The difference between simulation and reality will be different and its easy to chase numbers in the simulator.

Re: Transistor types in Bi-Pak AL60 modules?
 

C5 on my drawing does it make any difference?

Tubeglow.

Re: Transistor types in Bi-Pak AL60 modules?
 

C5 ? Do you mean the 3.9nf ?

Its normal practice to bypass the vbe multiplier transistor with a small electroylitic from C to E to ensure the loop gain of the amp is maintained at hf. The 3.9nf cap wouldn't do any harm but its not optimal.

Re: Transistor types in Bi-Pak AL60 modules?
 

If this is added to the sim will it sharpen the square wave response?

Tubeglow.

Re: Transistor types in Bi-Pak AL60 modules?
 

Yes, it clips cleanly which is good. Post #49,
https://www.vintage-radio.net/forum/...6&postcount=49

I must admit I didn't tweak the input bias for absolutely optimal symmetric clipping but that's easy to do of course in reality and in simulation by altering R3 (the 82k). I would alter that rather than the lower resistor simply because it maintains an equal input impedance between channels in a stereo pair with the 82k working into a cap at AC (C4)

Re: Transistor types in Bi-Pak AL60 modules?
 

Nope :)

The squarewave response is determined by a few things, but the main variables are the current available in the VAS stage (voltage amplifier stage). That's Q5 in the sim and R14 and R15 determine that mainly. Also the compensation networks, C8 and C9. And finally the input RF filter R1 and C10.

(Squarewave response is pretty decent actually for a design like this).

This is 1kHz off CD (any CD player will look identical) and the amp is way better than this. A slew rate of around 5 volts/us is all that is needed for full power output at 100watts into 8 ohms (that's 28 vrms or 80 volts pk/pk)

Re: Transistor types in Bi-Pak AL60 modules?
 

OK, that's me done for tonight methinks :)

Re: Transistor types in Bi-Pak AL60 modules?
 

OK,

Thank's for all the input.:D

Looks interesting.

Tubeglow.

Re: Transistor types in Bi-Pak AL60 modules?
 

Just had a quick look through some old transistor lists and found ZTX300 NPN and ZTX500 PNP. I haven't checked the full ratings of these transistors but in the interests of originality I may sub them into the design if I decide to construct a sibling for the module I have. I have a few 300 and 500s in my spares so if they do the job that would be good.
Alan.

Re: Transistor types in Bi-Pak AL60 modules?
 

The ZTX300 and ZTX500 were staples of the 1970s and 1980s hobby electronics world, and seemed to get used where something a bit more special than the run-of-the-mill BC107 was needed. I'm sure they'll do the job if the voltage ratings are OK.

Chris

Re: Transistor types in Bi-Pak AL60 modules?
 

Modified to use a complementary pair. Squarewave is at 50kHz.

Re: Transistor types in Bi-Pak AL60 modules?
 

I would build two new identical modules..use the BFS in the driver and try the ZTX or 2n...as the inputs. TIP41A drivers.
You will always be wondering if they are matched...save the worry build two..;D

I'm just wondering how good a job I can do with an etch pen..:-/
(Got to be worth a try)..Couple of pieces of fiberglass board..ferric and a brush for "Gentle help".

Tubeglow.