Bias Adjustment???

[Unit 148]

A questions for the experienced amp designers here.

My Metron HF 8 device amp has a single bias adjust for the four push-pull pairs of transistors.

Am I correct in that if all transistors are perfectly matched or at least share the same batch code then this single adjustment is probably more than OK.

My questions is would anything be gained in having bias adjustment for each push-pull pair of transistors?

Schematic on P.31 of the technical manual (third download link):

http://bama.edebris.com/manuals/metron/ma1000b-ms

Thanks.

Phil

 

[Toll_Free]

If you use parts from RF Parts, or get parts matched on a curve tracer (not just a hFE meter), then you probably will be OK.

I didn't pull the schematic up, but I'd put a diode from the CT of each input xformer to the bias supply to isolate each one.

Also, you know the #12 / XFORCE bias 'voodoo', I hope

--Toll_Free

 

[-=PEAKABOO=-]

Also, you know the #12 / XFORCE bias 'voodoo', I hope

--Toll_Free

LOL

 

[Toll_Free]

It's RRCB all over again!

 

[Unit 148]

Hi PEAKABOO,

This Phil in London, Uk.

How you doing.

Long time no speak.

As I mentioned above I still have an Xforce 16-pill that Dennis modded with his bias design.

I intend to get this out of storage and fire it up. In fact it's never been fired up so still new, if you can call 20+ years new

Would either of you happen to know what drive the 16 x 2879's require, that is for normal SSB use not balls to the wind?

Tnx

Phil
Unit 148

 

[Toll_Free]

Typical bias'ed usage, I see about 3-4 watts of carrier, with 12-15 PEP drive being normal, per transistor.

A 400 watt Teas tar provides MORE than enough drive to my Messenger in AB mode. A 500 or 667 does it to saturation in Class C mode.

--Toll_Free

 

[Unit 148]

I think that works out about right as this device has around 10dB gain so 12 in for 120 out in an ideal world.

Therefore unless one has a driver I cannot drive 16 pills from a typical ham HF transceiver with 100W output. I really need a 200W rig like the Kenwood 480 which runs 200W output and is mobile.

Better start saving.

Came across this little baby and thought it looked neat with semi surface mounted components: JUMA PA100 100 W Linear Amplifier

Click on the picks.

 

[Captain Kilowatt]

Came across this little baby and thought it looked neat with semi surface mounted components: JUMA PA100 100 W Linear Amplifier

Click on the picks.

I was interested in that until I saw the price. :blink: 400 Euros yowza!