6146, A, B, W and all other variants- great article. - UK Vintage Radio Repair and Restoration Discussion Forum

Cruisin Marine · 3rd Nov 2022, 12:33 am

I have just fired up an old Yaesu FT901DM After nearly 2 decades of it sitting redundant, and checked the neutralization and it is still fine

.
It uses two 6146B output valves.
I wondered whether if they go soft, what is the replacement situation... well here is invaluable info. on those series of valves and the variants, written by somebody who knows his onions.
https://www.tubesandmore.com/tech-ar...6-family-tubes

PS: If anyone is thinking of buying one of these FT901's, they are heavy and big old beasties, 18kg from memory, so start the weight lifting now so you can move it about!

Radio Wrangler · 3rd Nov 2022, 4:32 am

It's the 12BY7A that's the touchy one in several of the Yaesu transceivers. The circuit is designed around Toshiba ones and you might not be able to get others adjusted correctly. Infuriatingly on some sets you can't get TX drive and RX preselector to peak in the same place and they share the same knob!

The FT101ZD is a derivative of the 901, rather than the 101, it lacks the memory functions.

David

PA3DAF, Erwin · 3rd Nov 2022, 5:02 am

There is a lot of useful information, also about the final tubes, in the FT-901DM & FT-902DM survival guide.

Erwin, PA3DAF

G6Tanuki · 3rd Nov 2022, 9:34 am

The B variant has higher anode dissipation than the original 6146.

They tend to be driven rather hard in most ham transmitters..

Some transceivers from that era are known for a fault in the ceramic capacitors between the driver anode and the PA grid, they go leaky and so the bias on the PA starts to wander. Worst case it can cost you a pair of PA valves and a Mains transformer.

(yes, transmitters have the equivalent of 'that capacitor').

Cruisin Marine · 3rd Nov 2022, 1:14 pm

Thanks for that guide Erwin, it is most informative and mentions the 100pF/3kv coupling cap being a problem and repeats some of the info. from the article I referred to in my original post.
The importance of the driver valve is noted too, let's hope I don't have to do any valve swapping too soon.

G8UWM-MildMartin · 3rd Nov 2022, 2:10 pm

There is more information about the differences in construction between various types and makes and photographs of some at rated dissipation and more at:
http://k9axn.com/_mgxroot/page_10935.html
(The odd obvious mistakes include the heater rating for the S2001A.)

G6Tanuki · 3rd Nov 2022, 7:30 pm

I've got several 6146B/8298A here, acquired from a friend's two-way-radio business in Dallas/Fort-Worth in the early-80s when they were closing down their US 'low-band' [30-50MHz] network.

They're branded General Electric. I remember him telling me that the GE tubes were the only ones that would last when used in base-station/repeater service where they were expected to work lots-of-hours 24/7 in FM continuous-carrier service [a bit more arduous than the usual ICAS ham-radio duty]

I wonder who actually made the valves for GE, or did they make them themselves.

And I rather like their 1960s promo spiel on the cartons, "Progress is our most important product"

Cruisin Marine · 3rd Nov 2022, 8:10 pm

I wonder if anyone has pointers to the Toshiba and NEC (I have an NEC valve in my stock) datasheets for the 12BY7A if poss?
I can find the RCA and GE datasheets easily but not those.
Thanks.

3rd Nov 2022, 12:33 am	#1
Cruisin Marine Octode Join Date: Jul 2018 Location: Worthing, West Sussex, UK. Posts: 1,003	6146, A, B, W and all other variants- great article. I have just fired up an old Yaesu FT901DM After nearly 2 decades of it sitting redundant, and checked the neutralization and it is still fine . It uses two 6146B output valves. I wondered whether if they go soft, what is the replacement situation... well here is invaluable info. on those series of valves and the variants, written by somebody who knows his onions. https://www.tubesandmore.com/tech-ar...6-family-tubes PS: If anyone is thinking of buying one of these FT901's, they are heavy and big old beasties, 18kg from memory, so start the weight lifting now so you can move it about! __________________ "Behind every crowd, there's a silver Moonshine" Last edited by Cruisin Marine; 3rd Nov 2022 at 12:52 am.

3rd Nov 2022, 4:32 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: 6146, A, B, W and all other variants- great article. It's the 12BY7A that's the touchy one in several of the Yaesu transceivers. The circuit is designed around Toshiba ones and you might not be able to get others adjusted correctly. Infuriatingly on some sets you can't get TX drive and RX preselector to peak in the same place and they share the same knob! The FT101ZD is a derivative of the 901, rather than the 101, it lacks the memory functions. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

3rd Nov 2022, 5:02 am	#3
PA3DAF, Erwin Diode Join Date: Mar 2022 Location: Huissen, The Netherlands Posts: 9	Re: 6146, A, B, W and all other variants- great article. There is a lot of useful information, also about the final tubes, in the FT-901DM & FT-902DM survival guide. Erwin, PA3DAF

3rd Nov 2022, 9:34 am	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: 6146, A, B, W and all other variants- great article. The B variant has higher anode dissipation than the original 6146. They tend to be driven rather hard in most ham transmitters.. Some transceivers from that era are known for a fault in the ceramic capacitors between the driver anode and the PA grid, they go leaky and so the bias on the PA starts to wander. Worst case it can cost you a pair of PA valves and a Mains transformer. (yes, transmitters have the equivalent of 'that capacitor'). __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

3rd Nov 2022, 1:14 pm	#5
Cruisin Marine Octode Join Date: Jul 2018 Location: Worthing, West Sussex, UK. Posts: 1,003	Re: 6146, A, B, W and all other variants- great article. Thanks for that guide Erwin, it is most informative and mentions the 100pF/3kv coupling cap being a problem and repeats some of the info. from the article I referred to in my original post. The importance of the driver valve is noted too, let's hope I don't have to do any valve swapping too soon. __________________ "Behind every crowd, there's a silver Moonshine"

3rd Nov 2022, 2:10 pm	#6
G8UWM-MildMartin Heptode Join Date: Jan 2004 Location: Stockport, Greater Manchester, UK. Posts: 827	Re: 6146, A, B, W and all other variants- great article. There is more information about the differences in construction between various types and makes and photographs of some at rated dissipation and more at: http://k9axn.com/_mgxroot/page_10935.html (The odd obvious mistakes include the heater rating for the S2001A.)

3rd Nov 2022, 7:30 pm	#7
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: 6146, A, B, W and all other variants- great article. I've got several 6146B/8298A here, acquired from a friend's two-way-radio business in Dallas/Fort-Worth in the early-80s when they were closing down their US 'low-band' [30-50MHz] network. They're branded General Electric. I remember him telling me that the GE tubes were the only ones that would last when used in base-station/repeater service where they were expected to work lots-of-hours 24/7 in FM continuous-carrier service [a bit more arduous than the usual ICAS ham-radio duty] I wonder who actually made the valves for GE, or did they make them themselves. And I rather like their 1960s promo spiel on the cartons, "Progress is our most important product" Attached Thumbnails __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

3rd Nov 2022, 8:10 pm	#8
Cruisin Marine Octode Join Date: Jul 2018 Location: Worthing, West Sussex, UK. Posts: 1,003	Re: 6146, A, B, W and all other variants- great article. I wonder if anyone has pointers to the Toshiba and NEC (I have an NEC valve in my stock) datasheets for the 12BY7A if poss? I can find the RCA and GE datasheets easily but not those. Thanks. __________________ "Behind every crowd, there's a silver Moonshine"