6146B testing ? - UK Vintage Radio Repair and Restoration Discussion Forum

g4wim_tim · 16th Dec 2018, 7:27 pm

Hi,

I'm building an AM tx from scratch with a pair of 6146B's in the PA.

I have a pair of these valves but can't recall where I got them from or their history.

I was wondering if I should attempt to test them myself or if anyone local (ish) has a valve tester to check them over for me ?

I could vary the G1 bias fairly easily and measure the Anode current for a given screen voltage but not sure if this would show the true condition of the valve.

Regards Tim

Sean Williams · 16th Dec 2018, 7:34 pm

Hi Tim,

Probably best to just pop them in and have a go - so long as they pass some current, they will work in some capacity.

I've not really found DC testing to be that useful for a power valve - the anode current test would at least show that the valve is theoretically able to work.

ionburn · 16th Dec 2018, 8:06 pm

I did come across an article online from a ham who recommended building up to power, ie 'running in'. He came across premature failure if things were pushed too hard too fast. I am not sure if this is where I originally found it (I don't think so though) but this is a discussion I made note of: http://forums.qrz.com/index.php?thre...-tubes.293770/

M3VUV51 · 16th Dec 2018, 9:19 pm

Cant you find someone with an old 101ZD to try them in? Didn't the TS-520's use them as well?

M3VUV.

Aub · 16th Dec 2018, 9:30 pm

I would also suggest doing what Sean says. I built an AM TX, a few years ago, using 2 6146Bs in parallel. They should last a long time, as they only have about 430 V on the anodes and run about 80w DC input.

Go for it.

73s

Aub G4KQL

M3VUV51 · 16th Dec 2018, 9:35 pm

Just wondered if 572B's would be ok if the 6164 valves are shot? I got a pair for 30 quid, don't know if that's cheap?

g4wim_tim · 16th Dec 2018, 10:39 pm

Thanks for the replies guys - more or less in line with my thoughts.

I plan on running them in class C at about 100 watts DC in from 500V at 200mA and hope to get 60 - 70 watts RF carrier with no modulation - if the valves are anything like.

However as I'm going to be using high level anode / screen modulation I'm concerned about internal flash over on modulation peaks which could take out the anode RF choke for good measure.

I also have concerns about the anode tuning capacitor, but that is easily fixed.

In summary I'll start them with low drive / modulation and gradually ramp things up as I build confidence in the design and components or alternatively replacing stuff which breaks !

Regards Tim

TrevorG3VLF · 16th Dec 2018, 11:19 pm

I have a Heathkit transmitter with a screen modulated 6146. After many years of rest, I decided to try it out. There was a flash over so it was put back to rest. I have seen it that RF power valves should be woken up gently.

Some time back I tried to test a 6146 in a WW2 AVO tester. It went into oscillation, killing all RF signals in the locality and then tripping the overload.

I would suggest finding some working equipment to try them as a substitute.

Bazz4CQJ · 16th Dec 2018, 11:33 pm

I once tested the 6146's from my Kenwood TS530 using my Avo 163. No problems encountered and they gave good results.

B

ukcol · 17th Dec 2018, 9:31 am

6164B data sheet.

g4wim_tim · 17th Dec 2018, 11:13 am

Thanks ukcol

I had noticed the maximum anode voltage and noted that on speech peaks I would be exceeding the max rating by hitting maybe as high as 900V - hence my concern about flash over.

Perhaps I should revisit the choice of PA valve and select something with a little more head room voltage wise.

Back to the catalogues !

Regards Tim

g4wim_tim · 17th Dec 2018, 2:16 pm

Looks like what I'm building is very close to the Heathkit DX100 which uses a pair of 6146's with high level anode / screen modulation and an anode voltage of 740V so maybe I'm worrying over nothing.

Time will tell !

HamishBoxer · 17th Dec 2018, 2:40 pm

I think £30 for a pair of o/put valves is very fair.

G6Tanuki · 17th Dec 2018, 3:01 pm

I've used 6146s and their 25.2V-heater siblings in various HF drivers/amplifiers over the years.

They don't like being driven into much grid-current - and if you're using grid-resistor bias don't use more than around 25KOhms grid-resistor. They can be destroyed almost instantly if you lose the anode-voltage but the screen-voltage is still applied.

"Testing" them can be interesting: for typical amateur ICAS service they're driven quite hard and with age their cathode-emission falls away - in linear-amplifier service the symptom is distortion-causing 'flat-topping' well before you'd predict it to happen. A good one should be able to handle 300mA for a couple of seconds: I've seen some that struggle to achieve 100mA, which _will_ cause a nasty signal.

David Simpson · 17th Dec 2018, 5:37 pm

Contrary to Sean's point of view about DC testing Power Valves, I've been successfully DC testing & Gm graphing them for several years now. EL37's up to 117mA Ia, 807's, their American siblings - the VT136(very parasitic oscillation prone), and your particular range of 6146 American types(used by Sailor Radio in their range of AM HF Marine Tx's from the 60's & 70's). I always use ferrite beaded extension valve holders & Top Cap leads. And with CT160's & my Mk3.
For taking DC readings of Ia & Vg, always start with Low Ia/High Vg tabulations, then work your way slowly up the curve. As G6Tanuki says, only linger for a couple of seconds - just long enough to read those high Ia values - each time. This advice also stands for those folk testing O/P valves on a CT160 at full Ia. In my experience, CT160's are prone to PO, and RV2 - the -ve Vg Pot(very expensive to replace) does NOT like grid current being drawn.

Regards, David

g4wim_tim · 17th Dec 2018, 8:47 pm

Hi guys,

thanks for your tips - hopefully I won't destroy them but plan B is to buy a couple of NOS should the need arise.

FYI I'm posting pictures in the homebrew forum as things progress - just finished metal bashing on the PSU chassis.

Regards Tim

m0cemdave · 18th Dec 2018, 2:15 am

Quote:

Looks like what I'm building is very close to the Heathkit DX100 which uses a pair of 6146's with high level anode / screen modulation and an anode voltage of 740V so maybe I'm worrying over nothing.

6146's should be perfectly OK in AM service at 500V DC and 100mA per valve. Transmitters such as the KW Vanguard run happily at this level, with a single 6146 giving about 35W carrier output.
The RCA data book ICAS ratings give figures for a 600V plate modulated supply, which implies 1200V peaks.

g4wim_tim · 19th Dec 2018, 6:01 pm

Thanks for the confirmation Dave, hopefully there won't be too mnay flash overs !

BTW I used to live in Bletchley when I worked in Hanslope.

Regards Tim

16th Dec 2018, 7:27 pm	#1
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	6146B testing ? Hi, I'm building an AM tx from scratch with a pair of 6146B's in the PA. I have a pair of these valves but can't recall where I got them from or their history. I was wondering if I should attempt to test them myself or if anyone local (ish) has a valve tester to check them over for me ? I could vary the G1 bias fairly easily and measure the Anode current for a given screen voltage but not sure if this would show the true condition of the valve. Regards Tim __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.

16th Dec 2018, 7:34 pm	#2
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	Re: 6146B testing ? Hi Tim, Probably best to just pop them in and have a go - so long as they pass some current, they will work in some capacity. I've not really found DC testing to be that useful for a power valve - the anode current test would at least show that the valve is theoretically able to work. __________________ Engineers make things work and have spare bits when finished

16th Dec 2018, 8:06 pm	#3
ionburn Heptode Join Date: Dec 2014 Location: Lincoln, Lincolnshire, UK. Posts: 583	Re: 6146B testing ? I did come across an article online from a ham who recommended building up to power, ie 'running in'. He came across premature failure if things were pushed too hard too fast. I am not sure if this is where I originally found it (I don't think so though) but this is a discussion I made note of: http://forums.qrz.com/index.php?thre...-tubes.293770/

16th Dec 2018, 9:19 pm	#4
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: 6146B testing ? Cant you find someone with an old 101ZD to try them in? Didn't the TS-520's use them as well? M3VUV.

16th Dec 2018, 9:30 pm	#5
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: 6146B testing ? I would also suggest doing what Sean says. I built an AM TX, a few years ago, using 2 6146Bs in parallel. They should last a long time, as they only have about 430 V on the anodes and run about 80w DC input. Go for it. 73s Aub G4KQL __________________ Life's a long song, but the tune ends too soon for us all.

16th Dec 2018, 9:35 pm	#6
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: 6146B testing ? Just wondered if 572B's would be ok if the 6164 valves are shot? I got a pair for 30 quid, don't know if that's cheap?

16th Dec 2018, 10:39 pm	#7
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	Re: 6146B testing ? Thanks for the replies guys - more or less in line with my thoughts. I plan on running them in class C at about 100 watts DC in from 500V at 200mA and hope to get 60 - 70 watts RF carrier with no modulation - if the valves are anything like. However as I'm going to be using high level anode / screen modulation I'm concerned about internal flash over on modulation peaks which could take out the anode RF choke for good measure. I also have concerns about the anode tuning capacitor, but that is easily fixed. In summary I'll start them with low drive / modulation and gradually ramp things up as I build confidence in the design and components or alternatively replacing stuff which breaks ! Regards Tim __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.

16th Dec 2018, 11:19 pm	#8
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: 6146B testing ? I have a Heathkit transmitter with a screen modulated 6146. After many years of rest, I decided to try it out. There was a flash over so it was put back to rest. I have seen it that RF power valves should be woken up gently. Some time back I tried to test a 6146 in a WW2 AVO tester. It went into oscillation, killing all RF signals in the locality and then tripping the overload. I would suggest finding some working equipment to try them as a substitute.

16th Dec 2018, 11:33 pm	#9
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,934	Re: 6146B testing ? I once tested the 6146's from my Kenwood TS530 using my Avo 163. No problems encountered and they gave good results. B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

17th Dec 2018, 11:13 am	#11
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	Re: 6146B testing ? Thanks ukcol I had noticed the maximum anode voltage and noted that on speech peaks I would be exceeding the max rating by hitting maybe as high as 900V - hence my concern about flash over. Perhaps I should revisit the choice of PA valve and select something with a little more head room voltage wise. Back to the catalogues ! Regards Tim __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.

17th Dec 2018, 2:16 pm	#12
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	Re: 6146B testing ? Looks like what I'm building is very close to the Heathkit DX100 which uses a pair of 6146's with high level anode / screen modulation and an anode voltage of 740V so maybe I'm worrying over nothing. Time will tell ! __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.

17th Dec 2018, 2:40 pm	#13
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: 6146B testing ? I think £30 for a pair of o/put valves is very fair. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

17th Dec 2018, 3:01 pm	#14
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: 6146B testing ? I've used 6146s and their 25.2V-heater siblings in various HF drivers/amplifiers over the years. They don't like being driven into much grid-current - and if you're using grid-resistor bias don't use more than around 25KOhms grid-resistor. They can be destroyed almost instantly if you lose the anode-voltage but the screen-voltage is still applied. "Testing" them can be interesting: for typical amateur ICAS service they're driven quite hard and with age their cathode-emission falls away - in linear-amplifier service the symptom is distortion-causing 'flat-topping' well before you'd predict it to happen. A good one should be able to handle 300mA for a couple of seconds: I've seen some that struggle to achieve 100mA, which _will_ cause a nasty signal.

17th Dec 2018, 5:37 pm	#15
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Re: 6146B testing ? Contrary to Sean's point of view about DC testing Power Valves, I've been successfully DC testing & Gm graphing them for several years now. EL37's up to 117mA Ia, 807's, their American siblings - the VT136(very parasitic oscillation prone), and your particular range of 6146 American types(used by Sailor Radio in their range of AM HF Marine Tx's from the 60's & 70's). I always use ferrite beaded extension valve holders & Top Cap leads. And with CT160's & my Mk3. For taking DC readings of Ia & Vg, always start with Low Ia/High Vg tabulations, then work your way slowly up the curve. As G6Tanuki says, only linger for a couple of seconds - just long enough to read those high Ia values - each time. This advice also stands for those folk testing O/P valves on a CT160 at full Ia. In my experience, CT160's are prone to PO, and RV2 - the -ve Vg Pot(very expensive to replace) does NOT like grid current being drawn. Regards, David

17th Dec 2018, 8:47 pm	#16
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	Re: 6146B testing ? Hi guys, thanks for your tips - hopefully I won't destroy them but plan B is to buy a couple of NOS should the need arise. FYI I'm posting pictures in the homebrew forum as things progress - just finished metal bashing on the PSU chassis. Regards Tim __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.

19th Dec 2018, 6:01 pm	#18
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	Re: 6146B testing ? Thanks for the confirmation Dave, hopefully there won't be too mnay flash overs ! BTW I used to live in Bletchley when I worked in Hanslope. Regards Tim __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.