F5 power amplifier

[amp-guy]

Acrylic

Polycarbonate

once you have used polycarb you will never go back
no more chip outs or cracks

[fredlock]

So what about the bass? Middle of the road, lacking, non-existent? Or do you think its the smaller supply?

The bass is pretty good! I can't complain about it but I think you can make it better with the higher transformer rating IMHO.

[zinsula]

Hi Fredlock, some questions about your "transparent" amp:
- could you give me the rough dimensions of the heatsinks?
- are you biasing it as per the F5 article, i.e. 1.3A/MOSFET?
- how hot are your heat sinks getting?

I have similar sinks and thought they are insufficient, but maybe....

Thanks anyway
Tino

[tryonziess]

Just a little note about Lexan. You can bend it like you would sheetmetal and it will not crack. Makes really nice rounded corners.When you drill and tap lexan you can see the threads, they look kind of cool. Has fabulous other desirable characteristics. Just do not get it near acetone. Tad

[bubba177]

a little more about lexan-it is only rock resistant from punks-a good burglar always carries a cordless trimsaw to cut a nice sized hole

[tryonziess]

To Mr. Pass
Since you have gone to mostly TO-247 frame mosfets with most of your current designs, this one included, have you noticed any reliability issues as compared to the older TO-3 cases.
Being in the retail sector and using quite a few of these types of transistor should make you able to provide a quite accurate assumption.
Also, can you provide a rough percentage of beta test matches when purchased from a like lot number. I was quite happy with the results of my matching on my current project most of the units in a single tube fell into spec. Thanks Tad

[AMPMAN]

I have overshoot on the leading edge of the sqare wave of my f5 amp, also I cannot balance the voltage across the .47 resistors. the output voltage is ok but on one channel when I connect my signal generator the output goes to over 3 volts anybody?

[Nelson Pass]

Originally posted by tryonziess
Since you have gone to mostly TO-247 frame mosfets with most of your current designs, this one included, have you noticed any reliability issues as compared to the older TO-3 cases.

They work fine. I have not encountered any issues, however I don't send
product into corrosive environments, etc, nor do I operate the devices near
their maximum ratings.

Originally posted by AMPMAN
I have overshoot on the leading edge of the sqare wave of my f5 amp, also I cannot balance the voltage across the .47 resistors. the output voltage is ok but on one channel when I connect my signal generator the output goes to over 3 volts anybody?

A couple of possibilities - your generator might be putting out DC or might
be sending the amplifier into oscillation. The latter will occasionally occur if
the output of the amp becomes coupled to the input through a shared
ground or through capacitance between input and output cables.

There is a practical reason why we don't extend the bandwidth of amplifiers
beyond 100 KHz in PL products - too many issues in the field.

[fredlock]

- could you give me the rough dimensions of the heatsinks?

Tino,

There are 2 heatsinks per channel joined togehter. The dimension is approximately 9 1/2 " x 12 1/2" plus the add on 1/4" thickness aluminum bar mounted on the heatsink with the MOSFETS.

- are you biasing it as per the F5 article, i.e. 1.3A/MOSFET?

Yes.

- how hot are your heat sinks getting?

I did not measure the actual temperature but my assumption would be 35 to 40 degrees.

[jacco vermeulen]

Originally posted by fredlock
my assumption would be 35 to 40 degrees.

Checks out with the geometry and sizes you mention.

Your heatsinks look similar to the popular 30-rib 1.6" thick SK56 overhere.
A 5'' length of SK56 does 0.40C/W, makes 0.20 C/W for 10 inches, 25% added for rotating them 90 degrees gives 0.25C/W.
Corresponds to 35C-40C at an ambient temp of 20 to 25C.
Spacy, you could make a 100W F5 monaural block with that case.