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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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16th Dec 2018, 7:27 pm | #1 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
Posts: 232
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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
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Building and tinkering for over 50 years, from 807's to digital amateur TV. |
16th Dec 2018, 7:34 pm | #2 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
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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.
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16th Dec 2018, 8:06 pm | #3 |
Heptode
Join Date: Dec 2014
Location: Lincoln, Lincolnshire, UK.
Posts: 583
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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/
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16th Dec 2018, 9:19 pm | #4 |
Banned
Join Date: Feb 2018
Location: Horncastle, Lincolnshire, UK.
Posts: 203
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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 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,039
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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
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16th Dec 2018, 9:35 pm | #6 |
Banned
Join Date: Feb 2018
Location: Horncastle, Lincolnshire, UK.
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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?
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16th Dec 2018, 10:39 pm | #7 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
Posts: 232
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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
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Building and tinkering for over 50 years, from 807's to digital amateur TV. |
16th Dec 2018, 11:19 pm | #8 |
Rest in Peace
Join Date: Apr 2011
Location: Matlock, Derbyshire, UK.
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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 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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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
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17th Dec 2018, 9:31 am | #10 |
Rest in Peace
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Location: Harlaxton, Lincolnshire, UK.
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Re: 6146B testing ?
6164B data sheet.
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17th Dec 2018, 11:13 am | #11 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
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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
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17th Dec 2018, 2:16 pm | #12 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
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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 !
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Building and tinkering for over 50 years, from 807's to digital amateur TV. |
17th Dec 2018, 2:40 pm | #13 |
Dekatron
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Location: W.Butterwick, near Doncaster UK.
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Re: 6146B testing ?
I think £30 for a pair of o/put valves is very fair.
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17th Dec 2018, 3:01 pm | #14 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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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 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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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 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
Posts: 232
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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
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Building and tinkering for over 50 years, from 807's to digital amateur TV. |
18th Dec 2018, 2:15 am | #17 | |
Octode
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,223
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Re: 6146B testing ?
Quote:
The RCA data book ICAS ratings give figures for a 600V plate modulated supply, which implies 1200V peaks. |
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19th Dec 2018, 6:01 pm | #18 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
Posts: 232
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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
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Building and tinkering for over 50 years, from 807's to digital amateur TV. |