UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 22nd Jul 2019, 6:36 pm   #1
its ur aerial
Hexode
 
its ur aerial's Avatar
 
Join Date: May 2009
Location: Ryde, Isle of Wight, UK.
Posts: 418
Default Linear Amp using an 807

Does any one know of a circuit diagram for a small linear Amplifier using a single 807.
And would 550 - 600 volts of HT be enough?

Thanks
Ken, G6HZG
__________________
Life is not Hollywood, life is Cricklewood.
its ur aerial is offline  
Old 22nd Jul 2019, 6:52 pm   #2
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: Linear Amp using a 807

Higher HT generally gives greater linearity. I recall somewhere seeing a 1950s US design for a triode-strapped grounded-grid 807 linear, the big thing about GG operation is that it does away with the need for separate screen-supplies and neutralisation.

Some of the old US TV "Sweep Tubes" were essentially 807-derivatives, and these were popular for use in linear-amps.
G6Tanuki is offline  
Old 22nd Jul 2019, 6:56 pm   #3
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: Linear Amp using a 807

How much drive do you have?

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 23rd Jul 2019, 9:07 am   #4
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Linear Amp using a 807

Quote:
Originally Posted by G6Tanuki View Post
Higher HT generally gives greater linearity. I recall somewhere seeing a 1950s US design for a triode-strapped grounded-grid 807 linear, the big thing about GG operation is that it does away with the need for separate screen-supplies and neutralisation.

Some of the old US TV "Sweep Tubes" were essentially 807-derivatives, and these were popular for use in linear-amps.
There appear to be a number of examples on the net of this sort of thing. A 6L6 is electrically similar to the 807 except for the top cap. Other great valves would be the 6BG6 sweep tube as you say. See attached for 6L6 2MHz circuit, does require a moderately high drive voltage/power as I think David was alluding to.
Attached Thumbnails
Click image for larger version

Name:	807.jpg
Views:	637
Size:	38.3 KB
ID:	187207  
Argus25 is offline  
Old 23rd Jul 2019, 11:41 am   #5
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: Linear Amp using an 807

GG mode needs a fair bit more drive than grounded-cathode.

But as said, it gives good linearity and circumvents the need for neutralisation.

I'm guessing the wanted mode is SSB because of 'Linear' in the title.

6L6 and 807 are common in the UK. American sweep toobs are fairly rare. The PL509 and PL519 was the common line output family here and there are HF amp designs floating around using them ( EG: 'Frinear')

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 23rd Jul 2019, 4:55 pm   #6
its ur aerial
Hexode
 
its ur aerial's Avatar
 
Join Date: May 2009
Location: Ryde, Isle of Wight, UK.
Posts: 418
Default Re: Linear Amp using an 807

Thanks for the replies, it`s intended use is AM, on the VMARS net, driven by a 10 watt valve home brew TX, very similar to a Codar AT5.
__________________
Life is not Hollywood, life is Cricklewood.
its ur aerial is offline  
Old 23rd Jul 2019, 5:04 pm   #7
its ur aerial
Hexode
 
its ur aerial's Avatar
 
Join Date: May 2009
Location: Ryde, Isle of Wight, UK.
Posts: 418
Default Re: Linear Amp using an 807

I did find a circuit using the PL519/ 509, but I have not got a PL519, and the I recall the heater voltage being a bit high ? At the moment I have a Home brew PSU with 550 v DC HT and a 6.3 v LT.
I would also imagine PL519`s are getting a bit thin on the ground.
It` must be 30 years plus since I changed one in a Decca Bradford !

Ken G6HZG
__________________
Life is not Hollywood, life is Cricklewood.
its ur aerial is offline  
Old 23rd Jul 2019, 5:33 pm   #8
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: Linear Amp using an 807

Sounds like the 807 is the best bet.

Linear mode would be rather inefficient. Have you considered adding a modulator to the anode feed of the 807 and keeping it in class-C? I think you'll get a lot more bang for the buck.

David GM4ZNX
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 23rd Jul 2019, 7:55 pm   #9
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Question Re: Linear Amp using an 807

I see that alternative valves to the 807 have been mentioned. How about a pair of TT21? Are they still available? And typical prices, new & used?

Al.
Skywave is offline  
Old 23rd Jul 2019, 10:32 pm   #10
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Linear Amp using an 807

I'd go for a 6BG6 any day. These were one of RCA's first dedicated line scan valves, Brimar got the dies and made them too, so they are in the UK. AWV in Australia made them too. I see there is one on UK ebay now, they have a larger cathode surface area than an 807:

https://www.ebay.co.uk/itm/VINTAGE-B...gAAOSwEfVcTa~b
Argus25 is offline  
Old 23rd Jul 2019, 11:13 pm   #11
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: Linear Amp using an 807

TT21 are silly money being KT88 with top cap anode. You can get about ten NOS 807 for the price of one TT21.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 23rd Jul 2019, 11:27 pm   #12
m0cemdave
Octode
 
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
Default Re: Linear Amp using an 807

Quote:
Originally Posted by its ur aerial View Post
Thanks for the replies, it`s intended use is AM, on the VMARS net, driven by a 10 watt valve home brew TX, very similar to a Codar AT5.
Assuming that's 10W DC input like an AT5, you will be getting about 30W PEP in AM mode.

That would need a lot of 807's to get a useful increase in power (say 10dB, 300W PEP, 75W carrier). A couple of 813's would be more like it!

You'd be a lot better off just building a bigger AM Tx. How about the classic 2x 807 Class C finals, with 2x 807 in the modulator as Class B triodes, all running of 600 or 700V HT ? About 80 W carrier output (320W PEP fully modulated).
m0cemdave is online now  
Old 24th Jul 2019, 8:04 am   #13
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Linear Amp using an 807

Another solid option could be the PL38, if you don't mind a small transformer suited to the 30V heater. They have an anode dissipation similar to the 807 at 25W I think. The PL38 is certainly a very attractive valve.
Argus25 is offline  
Old 24th Jul 2019, 1:07 pm   #14
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: Linear Amp using an 807

As far as '807' linear-amp designs are concerned, it's worth remembering that the STC/Brimar 5B254M was essentially an 807 electrode-assembly fitted into a more-modern 'bottle' and base.

http://www.r-type.org/exhib/aab0149.htm

There are plenty of designs for 1950s/1960s linear-amp designs using the 5B254M in SWM, RadCom, the various RSGB handbooks etc - it could be worth seeking out a few of these for circuit-inspirations!

[Don't copy them slavishly though: the 5B254M and similar had shorter lead-out wires so significantly lower inter-electrode capacities. You may get away without neutralisation with one of these whereas the longer grid/cathode/screen-leadouts of an 807 could be sufficient to make it hoot impressively on the upper HF bands!]
G6Tanuki is offline  
Old 24th Jul 2019, 5:59 pm   #15
Mike. Watterson
Heptode
 
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
Default Re: Linear Amp using an 807

The FT101 series original used a TV LOPT valve, 6JS6A.
The later ones used 6146B, which while an Octal base, it's not pinch construction, but "really" button base.

I might have used an 807 in 1960s, but not today.
Mike. Watterson is offline  
Old 26th Jul 2019, 7:44 pm   #16
Restoration73
Nonode
 
Restoration73's Avatar
 
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
Default Re: Linear Amp using an 807

This circuit is also viable using a single 807 ;

https://www.qsl.net/vu2awc/ham_radio.../atn_qro-2.jpg
Restoration73 is offline  
Old 29th Jul 2019, 10:16 am   #17
boxdoctor
Rest in Peace
 
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
Default Re: Linear Amp using an 807

Re using a 6BG6 in this circuit : There is a meatier version, the 6CD6, in circulation, and I think they may be more common than the 6BG6. Tony.
boxdoctor is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:43 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.