Hi Paul,

Is cost an issue or do you just want to see if it can be done with
MOSFETs? About 25 years ago I did a small amp (25 watts or so) above
100MHz with FETs. But I found that cost was much higher as if I'd done
it bipolar. When I looked at 100W my then pretty puny budget made the
decision for me to go bipolar.

Personally I haven't seen much happening in cost/performance and I'd
probably start out bipolar. Another cost saver is if you leave the
supply voltage level a wildcard even if this is for a mobile app. It's
no big deal these days to create whatever voltage the transistors like
best from whatever is there as a supply.

I am still a big fan of tubes, as long as they are popular enough and
thus cheap. Transistors are rather fickle and a tiny glitch in the
load connection can send them to the greener grass in a millisecond.
Tubes brush this off in stride.

For rock bottom bill of materials budget it has always paid off to
check what TV manufacturers use in the horizontal deflection finals.
That's as low cost as it gets. But I guess with the advent of big
plasma screens that may fizzle over the next 10 years.

Regards, Joerg
http://www.analogconsultants.com

Joerg wrote:
For rock bottom bill of materials budget it has always paid off to
check what TV manufacturers use in the horizontal deflection finals.
That's as low cost as it gets. But I guess with the advent of big
plasma screens that may fizzle over the next 10 years.

Horizontal deflection transistors generally have an FT way too low
to be usefull much higher in frequency than the 160 or 80 meter ham
bands. Sweep tubes are now rare and expensive bottles costing more
than 'common' 6146 types. Surplus 1625 tubes used to be only a few
bucks each, can be found for about $5-10 each at hamfests and fleabay
(Still cheaper than 6146's though). 807's cost a little more.
The best bargin in price vs power might be the 811A, or the 813.

BTW I have a bunch of 813's I'd be willing to sell. Someone make me
a good offer on a lot of 5 of them. (Used, but don't look too bad).

Hi Ken,

It depends on the TV but all this has been 20+ years ago. In those days I
found a few transistors that made great shortwave amps. I believe their
part numbers pretty much all started with BU. When one type fell out of
favor with the TV manufacturers they showed up on markets by the carton.
Usually at dump shops or discounters.

The other types that worked even better were the video transistors that
drove the CRT. You had to secure a cheap source, no scavenging out of TVs
because each set only had three. But they were low power so that required
a soldering marathon and it only made sense when you could buy them a dime
a dozen. We used to do some crazy things such as running them oil cooled
because these weren't easy to mount on a heat sink.

Except for the CRT drivers the data sheets mostly didn't spec FT, just
switching times. But that used to be the same with small signal types such
as the BSS123 that I have used heavily in front ends.

Regards, Joerg
http://www.analogconsultants.com

On Wed, 05 May 2004 20:21:45 -0400, Ken Scharf
wrote:

BTW I have a bunch of 813's I'd be willing to sell. Someone make me
a good offer on a lot of 5 of them. (Used, but don't look too bad).

Nice. Got any KT88s?
--

The BBC: licenced at public expense to spread lies.

Hi Ken,

It depends on the TV but all this has been 20+ years ago. In those days I
found a few transistors that made great shortwave amps. I believe their
part numbers pretty much all started with BU. When one type fell out of
favor with the TV manufacturers they showed up on markets by the carton.
Usually at dump shops or discounters.

The other types that worked even better were the video transistors that
drove the CRT. You had to secure a cheap source, no scavenging out of TVs
because each set only had three. But they were low power so that required
a soldering marathon and it only made sense when you could buy them a dime
a dozen. We used to do some crazy things such as running them oil cooled
because these weren't easy to mount on a heat sink.

Except for the CRT drivers the data sheets mostly didn't spec FT, just
switching times. But that used to be the same with small signal types such
as the BSS123 that I have used heavily in front ends.

Regards, Joerg
http://www.analogconsultants.com

On Wed, 05 May 2004 20:21:45 -0400, Ken Scharf
wrote:

BTW I have a bunch of 813's I'd be willing to sell. Someone make me
a good offer on a lot of 5 of them. (Used, but don't look too bad).

Nice. Got any KT88s?
--

The BBC: licenced at public expense to spread lies.

Joerg wrote:
For rock bottom bill of materials budget it has always paid off to
check what TV manufacturers use in the horizontal deflection finals.
That's as low cost as it gets. But I guess with the advent of big
plasma screens that may fizzle over the next 10 years.

Horizontal deflection transistors generally have an FT way too low
to be usefull much higher in frequency than the 160 or 80 meter ham
bands. Sweep tubes are now rare and expensive bottles costing more
than 'common' 6146 types. Surplus 1625 tubes used to be only a few
bucks each, can be found for about $5-10 each at hamfests and fleabay
(Still cheaper than 6146's though). 807's cost a little more.
The best bargin in price vs power might be the 811A, or the 813.

BTW I have a bunch of 813's I'd be willing to sell. Someone make me
a good offer on a lot of 5 of them. (Used, but don't look too bad).