Veronica Amp

Everything technical about radio can be discussed here, whether it's transmitting or receiving. Guides, charts, diagrams, etc. are all welcome.
Post Reply
geegosh
who u callin ne guy bruv
who u callin ne guy bruv
Posts: 11
Joined: Sun Mar 06, 2016 1:11 pm

Veronica Amp

Post by geegosh » Wed Aug 30, 2017 4:05 pm

Hi all :tup

I just picked up a job lot off eBay (sure a few of you may have seen this listing)

Veronica 5W TX,
Veronica / JIVA 30W Amp
Stereo Encoder & PSU - all for under £60 which I thought wasn't too bad!

Just got a small question with the amp, it states max. power input is 5W on the old Veronica site. I need some re-assurance that there's no min. power input either to drive this thing, their documentation is quite hard to interpret. It states the minimum power output on final stage is 30W..... but I doubt it will chuck out 30W if I use with 1W drive...?

http://www.veronica-kits.co.uk/30wpa.htm

Basically my question; can I drive this amp with a 1W board, ignoring the fact I've got a 5W board anyway, without any serious risks to the amp / my output?

Cheers
G

MiXiN
proppa neck!
proppa neck!
Posts: 612
Joined: Sun Sep 07, 2014 4:20 pm

Re: Veronica Amp

Post by MiXiN » Wed Aug 30, 2017 4:51 pm

He listed that lot on eBay for £39 a couple of weeks ago, but then took it down and relisted at the price you bought it for about a week or so ago.

A 1W drive will be fine and won't harm anything whatsoever, so just give it a try and see what power you get out of the amplifier.

The specification claims that the amp' has 14DB gain, so off the top of my head, 1W into it should be around 25W out.

geegosh
who u callin ne guy bruv
who u callin ne guy bruv
Posts: 11
Joined: Sun Mar 06, 2016 1:11 pm

Re: Veronica Amp

Post by geegosh » Wed Aug 30, 2017 5:08 pm

Did he :| Bloody nora, typical.

Ah well, I guess I've paid £15 for each item, provided it all checks out.... it isn't a bad price. What's the verdict on the amps? That's what I was mainly interested in, the rest not so much. The TX looks a pain to tune with no PLL..

Cheers for the heads up! Will post back here when I've received the lot.

Albert H
proppa neck!
proppa neck!
Posts: 2737
Joined: Tue Apr 05, 2016 1:23 am

Re: Veronica Amp

Post by Albert H » Thu Aug 31, 2017 2:27 am

As I remember,those PAs have 2N6083 or 2N6084 power transistors in them. The amplifier probably won't do much with 1 Watt of drive - you might not even get your Watt out! If you put 5 Watts into it, it should do about 30 Watts out. These are very old RF power transistors (from the 1970s) back from the days when 6dB of gain was thought to be a lot. They have the advantage that they're reasonably robust - they're quite difficult to blow up!

Back when I first started building transistorised VHF FM rigs, we used to assume that low level stages in the exciter would have (roughly) 10dB gain per stage - that's 10 X power gain. 1mW would be amplified to 10mW, 10mW to 100mW and so on. A typical rig in those days would have many more stages than one today:

We used to start at ¼f - so the oscillator would be between 22 and 27 MHz. I preferred the Colpitts oscillator, though others would use Clapp or even Vackar circuits. This would then go through an un-tuned buffer stage to provide some isolation between the oscillator and subsequent stages, into the first frequency doubler stage. This would get us to ½f, and would be critically tuned. There would then be a second doubler to get to the output frequency. I used double-tuned filtering at this point to ensure that I had really clean drive. All the transistors up to this point would have been either BSX20 or BF494. The output of the second doubler would be around 10mW of the required output frequency. This would go to a BSX20 amplifier stage, giving about 100mW. This final BSX20 would need a little heatsink.

The 100mW driver would usually be separately boxed, and would usually have its own 12V regulator. The next stage would get us up to about a Watt, using either a 2N4427 or a 2N3866 according to the supply voltage of the rig - battery powered stuff was usually run at 13V8, and mains powered rigs could have the luxury of 28V supplies. Assuming we're at 13V8, the next stage would be something like a PT8810 or a 2N6081 to get to about 8 Watts, and the final would be a 2N6084 for around 40 Watts.

If we were at 28V, the stage gain would be higher, and we'd use a 2N3375 into a weird little stud-mounted device called a 587BLY. I built huge numbers of PAs with the 3866, 3375, 587BLY line-up. They were entirely consistent - three stages would take 100mW in and give 90 Watts out at 28V supply. If you could give it a bit more supply voltage, you could get the magic 100 Watts. I also built large numbers of PAs with pairs of 587BLYs or even four paralleled for nearly 200 Watts! Other favourite devices were the SD1019 and SD1127 which were (sort of) second generation devices, with more power gain, but were much more expensive.

These days, we're spoilt. I have a PA on the bench at the moment that needs just 4 Watts of drive for 1500 Watts output - no-tune, high efficiency and just a single stage! My current basic rig design uses an at-frequency oscillator that develops 800mW in a single stage. This drives a single small 12V FET for powers between 4 and 18 Watts (according to requirement). It's almost like the old valve days, when we could develop high powers with just two or three active devices!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

geegosh
who u callin ne guy bruv
who u callin ne guy bruv
Posts: 11
Joined: Sun Mar 06, 2016 1:11 pm

Re: Veronica Amp

Post by geegosh » Thu Aug 31, 2017 9:20 pm

Albert H wrote: Thu Aug 31, 2017 2:27 am As I remember,those PAs have 2N6083 or 2N6084 power transistors in them. The amplifier probably won't do much with 1 Watt of drive - you might not even get your Watt out! If you put 5 Watts into it, it should do about 30 Watts out. These are very old RF power transistors (from the 1970s) back from the days when 6dB of gain was thought to be a lot. They have the advantage that they're reasonably robust - they're quite difficult to blow up!

Back when I first started building transistorised VHF FM rigs, we used to assume that low level stages in the exciter would have (roughly) 10dB gain per stage - that's 10 X power gain. 1mW would be amplified to 10mW, 10mW to 100mW and so on. A typical rig in those days would have many more stages than one today:

We used to start at ¼f - so the oscillator would be between 22 and 27 MHz. I preferred the Colpitts oscillator, though others would use Clapp or even Vackar circuits. This would then go through an un-tuned buffer stage to provide some isolation between the oscillator and subsequent stages, into the first frequency doubler stage. This would get us to ½f, and would be critically tuned. There would then be a second doubler to get to the output frequency. I used double-tuned filtering at this point to ensure that I had really clean drive. All the transistors up to this point would have been either BSX20 or BF494. The output of the second doubler would be around 10mW of the required output frequency. This would go to a BSX20 amplifier stage, giving about 100mW. This final BSX20 would need a little heatsink.

The 100mW driver would usually be separately boxed, and would usually have its own 12V regulator. The next stage would get us up to about a Watt, using either a 2N4427 or a 2N3866 according to the supply voltage of the rig - battery powered stuff was usually run at 13V8, and mains powered rigs could have the luxury of 28V supplies. Assuming we're at 13V8, the next stage would be something like a PT8810 or a 2N6081 to get to about 8 Watts, and the final would be a 2N6084 for around 40 Watts.

If we were at 28V, the stage gain would be higher, and we'd use a 2N3375 into a weird little stud-mounted device called a 587BLY. I built huge numbers of PAs with the 3866, 3375, 587BLY line-up. They were entirely consistent - three stages would take 100mW in and give 90 Watts out at 28V supply. If you could give it a bit more supply voltage, you could get the magic 100 Watts. I also built large numbers of PAs with pairs of 587BLYs or even four paralleled for nearly 200 Watts! Other favourite devices were the SD1019 and SD1127 which were (sort of) second generation devices, with more power gain, but were much more expensive.

These days, we're spoilt. I have a PA on the bench at the moment that needs just 4 Watts of drive for 1500 Watts output - no-tune, high efficiency and just a single stage! My current basic rig design uses an at-frequency oscillator that develops 800mW in a single stage. This drives a single small 12V FET for powers between 4 and 18 Watts (according to requirement). It's almost like the old valve days, when we could develop high powers with just two or three active devices!
Cheers Albert, I guess that this design must be slightly different to some of the other older JIVA amps? As their 12W model for example only needed 1W drive, same with the 25W amp too I believe.

I'll experiment driving it at different power levels and measure output, and post results back here.

User avatar
sinus trouble
proppa neck!
proppa neck!
Posts: 1410
Joined: Fri Aug 22, 2014 11:34 pm

Re: Veronica Amp

Post by sinus trouble » Thu Aug 31, 2017 10:35 pm

Nice purchase Mr Gosh!
Im not gonna lie, Im kinda jealous Haha! :D
It would be great to see any pics of this classic gear!
I am as stupid as I look! :|

Post Reply