The New AB1 GG 4-1000A Linear Amp - Regulated Screen and Grid

[Opcom]

Just another lin amp for fun. 2 x QB 5/1750 ,  200 watts  ( for fillament and drive power. )  Va = 5kV  Ia = 1A peak

Those are  the 'finals' supposed to be used in the Philips 2KVA audio amp here. It will have to be 4-1000's or something here.

The QB5/1750 should be interesting to hams because it uses a large grid bias unlike the 3-500 or 3-1000 and it also requires only simple fan cooling, no special arrangements. The plate connection is a 9.5mm solid rod for better heat removal. It's a big tube but has a 500W dissipation, built like a tank.

[Opcom]

Thanks for these details!

I am not thinking of building one of these big 2-tube amps, but a 1-tube is possible and should be OK for AM. I don't have a steady supply of good 4-1000's.

I found one of those B&W tanks, It ought to be enough. Made for KW DC, right? There is also a 2KVA plate transformer here.

I would like to make something physically like the old Elenco Commander, if I could find the schematic, but improve it with the screen and bias, like in your amp and run AB1. No grid current plus 'low'gain to avoid working VHF.

I would like to see the  11N90 MOSFET screen regulator schematic, I see something's been posted, I need to look at it. I'm interested in the input tuning too, to keep things cleaner.

The goal is to replace the NCL-2000. It is a fine amp but not best for AM.



It's as well to repeat the specs on those 5 blade fans from ebay since you say they are less noisy. Ball bearings means long life too.

Dimensions (As Pictured)   Electrical
Height   4.75"   Voltage   115 VAC
Width   4.75"   Motor RPM   2800
Depth   1.5"   Motor Watts   18
Operating Life   10,000 Hrs.   Motor Amps   .2

Thank you,
Patrick

[W1VD]

T

Yes ... good to cross paths again OM.

In the end I was IMD limited by the transceiver (K3) driving the amplifier ... couldn't look much below -38 dB IM3. Started at Q = 1.0 (knowingly too low) and was working my way up to Q levels >3 ... lack of time and the need to get it on the air (for Es season) cut further testing short.  It was rather inconvenient testing as the components in the input pi net were fixed and had to be changed out for subsequent tests. Your mention of the roller inductor in your amplifier peaked my interest ... as I think you have a 'real time' IMD test setup.

As far as the 'chain' effect ... if there's some clean drive to spare one could insert a power attenuator between the xcvr and the amplifier to 'dampen' the effects of the amplifier input match tuning.

Anyway, figured this testing might dovetail with your eternal quest for lower and lower IMD levels. Wish others were as interested in this aspect of transceiver/power amplifiers ... especially on 6 meters! There are some really crappy signals on that band.       

[Tim WA1HnyLR]

Hi Thomas,
Excellent on the White Barry White, It is now time to build a BIG SBE rig,
Tim WA1HnyLR

[K1JJ]

Hi Thomas,
Excellent on the White Barry White, It is now time to build a BIG SBE rig,
Tim WA1HnyLR

Yo Tron!


I always wanted to build an 833A SBE, but yours provides plenty of on-air puking for both of us....  

Can you come up with a good name?   Maybe something that refers to a drunk as he SBE/weaves down the street.


I'm making a cabinet for the White Barry White now. Then the panel lettering and testing. Shud have it on the air soon.  Seez ya then.


T

[W2VW]

Use a lab sig gen to provide carrier. A little PM can be added for SBE.

[Opcom]

Can you come up with a good name?   Maybe something that refers to a drunk as he SBE/weaves down the street.

how about a free for all to suggest names..

"Harvey Sidebanger"

"Ethanol Viper" got to keep an alcohol theme??


welcome to the drunken style kung fu of radio.

so how much 'deviation' has to be added for the desired noise reduction while remaining plausibly deniable in the culpability department?  deviants.

[K1JJ]

Here's some pics of the completed unit. Got the panel lettered, cables tie wrapped and cabinet built and painted.

Total self-contained except for the HV power supply.

Still need to test everything and put the cabinet on.  

I decided to call it "Rico Suave II."      The original Rico was the class E rig. That is torn down, though may be back on the air soon with another ham.

Rico Suave:
http://www.youtube.com/watch?v=jKT-o7fg2Rg


Pics:  I added a C2 loading 160M .002 uf padding cap and relay.  Coverage down to 1800 Khz.

Rico is quite a handsome amp in person - the pics don't do justice. Using the caster wheels, Rico can dance well too.

T

[K1JJ]

Here's the aluminium cabinet - just painted today.   I'll take a shot with it all together soon.

That's the front and rear view.  I plan to add handles. The cabinet slides off in seconds for easy servicing.  The HV is completely blocked off for safety when the cabinet is in place.


T

[W2VW]

Hey Tom,

    Do you do anything to try to cure the paint or just enjoy the scent? I'm asking because I have a pair of racks which will soon be spray painted to match the rest of the stuff in the new shack.

DC

[KB2WIG]

I think that a classie chassie needs a demure, but at the same time, stylish accessory.


klc

[K1JJ]

Hey Tom,

    Do you do anything to try to cure the paint or just enjoy the scent? I'm asking because I have a pair of racks which will soon be spray painted to match the rest of the stuff in the new shack.

DC

Hi Dave,

I just spray it outside on the stone driveway and let the sun bake it for a day or two.  It dries to the touch within 2 minutes, so no dust sticks.   There appears to be little to no outgassing after 2 days in the sun. 

I use ACE Hardware sprays, probably a lacquer based paint.  My cabinet choice is wildflower blue, satin gloss.


What color are you matching up?

T

[W2VW]

Thanks Tom. That's roughly what I will be doing. Matching some semi-gloss black.

[K1JJ]

Today I slid the cabinet on and tuned up Rico Suave II on 160, 75 and 40M to run some initial tests.  Dummy load of course.

I found it ran best at about 400V of regulated screen voltage .  Also, 50 watts of carrier drive gives about 20ma of screen current, 10ma of grid current and about 2000 watts of output.  That's about 16dB of gain, not bad. This is FB, since the grid is drawing little current, even in GG, thus better IMD figures.  At 500 watts carrier, there is no screen or grid current at all.

I have the amp biased to slightly below cut-off to take advantage of the class C efficiency effect.  At 500 watts of carrier there is barely a glow on the plates.

With 4KV, the amp will do an easy 2500 watts pep. So, running it at 400 watts of carrier will give plenty of headroom for X6 audio overhead reserve.

To my dismay, on 40M I found at certain input tuning and output tuning settings it took off - was unstable.  I realized I forgot to add the old GFZ trick and put in a 100pf in series with a 100 ohm 2 watt resistor across one filament pin to ground for each tube. This loads the filament choke for VHF parasitics. That did the job and now the amp is completely stable, at least from 160 - 40M.

I still need to run some 2-tone IMD tests, but because the screen voltage keeps the grid current down, I expect the amp to be at least -35 dB 3rd or better running at this conservative level. After all, ONE tube will do 500 watts carrier at 2500 w pep - with a higher voltage....

Both the input and tank roller inductors are working well. I can easily match 1:1 on the input. I find that the tank inductor gets luke warm after an old buzzard, but not excessively.  I can set tank C1-L1-C2 to the desired band rather quickly using the turns counters. The presets are written down and efficient.


I need to monitor tube exit temperature to see how the quiet muffin fans make out, but so far it seems to stay quiet and cool at 400 watts carrier out. Driven by the FT-1000D, this is my "fast get on the air- switch bands" rig.

It uses the common 6-step sequencer system as Fabio II. However, I'm using just the HV, ant relay and audio steps for it.  It was easily integrated into the station and fast to select for use.  I really like this amp and hope to use it often.

Look at the pic below and you will see the op position is getting crowded. I am surrounded by white Fabios, Rico Suaves and Dr. Loves.  The making of a good B horror flick..  

T

[K1JJ]

***   BTW,  Here's the 4-1000A plate modulated by a pair of 4-1000As project:

http://amfone.net/Amforum/index.php?topic=33816.0


And the view of two 4X1's in cascade: