Good day all!
I've been having some problems with my 820s. It was fine for several
years and then I had a flashover in the finals. This may have been due
to a faulty ground on a "UHF" coax connector.
Have replaced the finals with 12 volt 6146B's (putting the heaters in
parallel of course). However although it now works, its effeciency is
damned awful. When it is loaded up to give 60 watts RF into a dummy load
the dissappation in 6146 anodes makes then glow cherry red!!!
Now my info tells me that the 6146B is rated at 30 watts anode
dissappation per tube (total 60 watts) so based on my 50 odd years of
electronics wouldn't expect a red hot anode at anything like the
theoretical 66% efficiency.
Yes, I have replaced the anode coupling cap (with an appropriate 3Kv rf
type) checked all the tube voltages set up the neutralisation and tried
the rig on all bands to ensure that the padding caps are OK. Same result!
My thinking is that my 6146B's may be in poor condition. Unfortunately
My old Heath valve tester does not do a very good job on big power
valves so although it says they are OK I don't really trust it.
So far I can't locate any parasitics up to about 120 MHz either.
Anyone had a similar problem? I am getting so fed up with it that I'm
thinking of running with 1x6146 and building a small linear amp
~400watts to drive the antennas.
Regards Cliff Wright ZL1BDA ex G3NIA.

Hello,


On 28 Ago, 07:05, cliff wright wrote:
Good day all!
I've been having some problems with my 820s. It was fine for several
years and then I had a flashover in the finals. This may have been due
to a faulty ground on a "UHF" coax connector.
Have replaced the finals with 12 volt 6146B's (putting the heaters in

what exactly are "12 volt 6146B's" ?
6146B have 6.3V heater. What tube are you using exactly?

73
Francesco IZ8DWF

wrote:

what exactly are "12 volt 6146B's" ?
6146B have 6.3V heater. What tube are you using exactly?

There were several variants with different heater voltages. I once
bought a bunch of them cheaply at a hamfest. If you were building
your own rig and could set the heater voltage, they were well worth
the price.

In a commerical radio, e.g. the 820, they were of absolutely no
use.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

On 28 Ago, 11:59, (Geoffrey S. Mendelson) wrote:
wrote:
what exactly are "12 volt 6146B's" ?
6146B have 6.3V heater. What tube are you using exactly?

There were several variants with different heater voltages. I once
bought a bunch of them cheaply at a hamfest. If you were building
your own rig and could set the heater voltage, they were well worth
the price.


yes, I remember, but afair they had different "names", surely not
marked as 6146B.

73
Francesco IZ8DWF

Geoffrey S. Mendelson wrote:
wrote:


what exactly are "12 volt 6146B's" ?
6146B have 6.3V heater. What tube are you using exactly?


There were several variants with different heater voltages. I once
bought a bunch of them cheaply at a hamfest. If you were building
your own rig and could set the heater voltage, they were well worth
the price.

In a commerical radio, e.g. the 820, they were of absolutely no
use.

Geoff.


The tubes in Question are a pair of 6883B's. According to all my data
they are identical to the 6146B except for a nominally 12.6 volt
heater rating, and a tiny increase in interelectrode capacity (about
1%). They were often used in high power (~60 watt) HF "bush" radio
telephones in NZ until recently, both in SSB and AM modes.
So they are relatively common here.
I pulled the covers off the final to check after your posting.
Since the 820S actually runs the 6146B heaters in series from 12.6 volts
there should be absolutely NO reason why they couldn't do the job with a
simple heater rewire from series to parallel.
They are physically identical to a 6146B externally.
Hope this clarifies the situation.
Regards Cliff Wright ZL1BDA

On 28 Ago, 13:11, cliff wright wrote:
Geoffrey S. Mendelson wrote:

The tubes in Question are a pair of 6883B's. According to all my data
they are identical to the 6146B except for a nominally 12.6 volt
heater rating, and a tiny increase in interelectrode capacity (about
1%). They were often used in high power (~60 watt) HF "bush" radio
telephones in NZ until recently, both in SSB and AM modes.
So they are relatively common here.
I pulled the covers off the final to check after your posting.
Since the 820S actually runs the 6146B heaters in series from 12.6 volts
there should be absolutely NO reason why they couldn't do the job with a
simple heater rewire from series to parallel.
They are physically identical to a 6146B externally.

Indeed the 6883B is like a 6146B with different heater voltage. Then
either these tubes are bad or you have another problem on your radio.
Check antenna TX/RX relay and antenna socket connector. I had an
FT-102 with antenna socket with an intermittent solder joint and it
caused all sort of problems. It seems that you already checked all
voltages on the tubes, but it might help to know what you exactly
measured on the various grids and anodes, both in RX mode and in TX
(idle). Do you observe any variation on the idle current of tubes when
in TX mode with no mic input? When these tubes fail usually they have
an ever increasing idle current and there's little to no way to stop
this current to increase.

73

Francesco IZ8DWF

"cliff wright" wrote in message
...
Good day all!
Have replaced the finals with 12 volt 6146B's (putting the heaters in
parallel of course). However although it now works, its effeciency is
damned awful.

That should work fine.

When it is loaded up to give 60 watts RF into a dummy load
the dissappation in 6146 anodes makes then glow cherry red!!!

Does maximum power out perfectly coincide with the dip in plate
current? What is the quiescient plate idle current in SSB? What
is the grid drive current when tuning? Are you using a terminating
type dummy load wattmeter, or an inline wattmeter to an antenna?

What is the plate current when tuned for 60 watts output?

Yes, I have replaced the anode coupling cap (with an appropriate 3Kv rf
type)

That wouldn't be a likely cause.,,

checked all the tube voltages set up the neutralisation and tried
the rig on all bands to ensure that the padding caps are OK.

Double check you coax jumper cables for problems, unsoldered
shields, etc. Sometimes simple solutions to difficult problems
elude us.

Peter k1zjh

On Aug 28, 1:05 am, cliff wright wrote:
Good day all!
I've been having some problems with my 820s. It was fine for several
years and then I had a flashover in the finals. This may have been due
to a faulty ground on a "UHF" coax connector.
Have replaced the finals with 12 volt 6146B's (putting the heaters in
parallel of course). However although it now works, its effeciency is
damned awful. When it is loaded up to give 60 watts RF into a dummy load
the dissappation in 6146 anodes makes then glow cherry red!!!
Now my info tells me that the 6146B is rated at 30 watts anode
dissappation per tube (total 60 watts) so based on my 50 odd years of
electronics wouldn't expect a red hot anode at anything like the
theoretical 66% efficiency.
Yes, I have replaced the anode coupling cap (with an appropriate 3Kv rf
type) checked all the tube voltages set up the neutralisation and tried
the rig on all bands to ensure that the padding caps are OK. Same result!
My thinking is that my 6146B's may be in poor condition. Unfortunately
My old Heath valve tester does not do a very good job on big power
valves so although it says they are OK I don't really trust it.
So far I can't locate any parasitics up to about 120 MHz either.
Anyone had a similar problem? I am getting so fed up with it that I'm
thinking of running with 1x6146 and building a small linear amp
~400watts to drive the antennas.
Regards Cliff Wright ZL1BDA ex G3NIA.

Cliff -
You mean "wired in parallel".

A flashover in the final compartment can take out other things. You
may have a failed plate choke, a leaky/lossy blocking capacitor, etc.
Often the damage is visible (as in "plate choke is on fire" or
"coupling capacitor looks like a burnt black potato chip") but other
times it is not so visible - e.g. arcover inside the plate choke that
makes it look OK from the outside, may even give the same DC
resistance on an ohmmeter, but completely negates its usefulness in
letting the plates swing at RF.

You don't say what your 12V 6146's are (you keep on calling them
6146B's but obviously they cannot be), but some of them are not
directly drop-in, they require not just tweaking the neutralization
but a change in biasing. I'd expect if you're truly putting 60W out,
that you can look at the power in (Volts times Amps) and figure out if
the dissipation should be making them glow red or not. It's possible
the metering circuitry got fried in the arcover too (some meter the
cathode current, some meter the plate current, but in either case the
resistors used as meter shunts can go wrong, or sometimes the chokes
and bypass caps between the final compartment and the meter can go bad
too.)

If the plates are going red with what you think ought to be just idle
bias on the tubes, then you either have a bias problem, a metering
problem, or a nasty runaway parasitic, or all three! Often these
symptoms do not arrive in isolation but in threes!

Tim.

Tim Shoppa wrote:
On Aug 28, 1:05 am, cliff wright wrote:

Good day all!
I've been having some problems with my 820s. It was fine for several
years and then I had a flashover in the finals. This may have been due
to a faulty ground on a "UHF" coax connector.
Have replaced the finals with 12 volt 6146B's (putting the heaters in
parallel of course). However although it now works, its effeciency is
damned awful. When it is loaded up to give 60 watts RF into a dummy load
the dissappation in 6146 anodes makes then glow cherry red!!!
Now my info tells me that the 6146B is rated at 30 watts anode
dissappation per tube (total 60 watts) so based on my 50 odd years of
electronics wouldn't expect a red hot anode at anything like the
theoretical 66% efficiency.
Yes, I have replaced the anode coupling cap (with an appropriate 3Kv rf
type) checked all the tube voltages set up the neutralisation and tried
the rig on all bands to ensure that the padding caps are OK. Same result!
My thinking is that my 6146B's may be in poor condition. Unfortunately
My old Heath valve tester does not do a very good job on big power
valves so although it says they are OK I don't really trust it.
So far I can't locate any parasitics up to about 120 MHz either.
Anyone had a similar problem? I am getting so fed up with it that I'm
thinking of running with 1x6146 and building a small linear amp
~400watts to drive the antennas.
Regards Cliff Wright ZL1BDA ex G3NIA.


Cliff -
You mean "wired in parallel".

A flashover in the final compartment can take out other things. You
may have a failed plate choke, a leaky/lossy blocking capacitor, etc.
Often the damage is visible (as in "plate choke is on fire" or
"coupling capacitor looks like a burnt black potato chip") but other
times it is not so visible - e.g. arcover inside the plate choke that
makes it look OK from the outside, may even give the same DC
resistance on an ohmmeter, but completely negates its usefulness in
letting the plates swing at RF.

You don't say what your 12V 6146's are (you keep on calling them
6146B's but obviously they cannot be), but some of them are not
directly drop-in, they require not just tweaking the neutralization
but a change in biasing. I'd expect if you're truly putting 60W out,
that you can look at the power in (Volts times Amps) and figure out if
the dissipation should be making them glow red or not. It's possible
the metering circuitry got fried in the arcover too (some meter the
cathode current, some meter the plate current, but in either case the
resistors used as meter shunts can go wrong, or sometimes the chokes
and bypass caps between the final compartment and the meter can go bad
too.)

If the plates are going red with what you think ought to be just idle
bias on the tubes, then you either have a bias problem, a metering
problem, or a nasty runaway parasitic, or all three! Often these
symptoms do not arrive in isolation but in threes!

Tim.

Hi Guys!
Well I got a chance to look at the TS820S today and solved at least some
of the mystery. When I had the flashover the meter went O/C so i had to
replace it with a simlar meter with the original face.
Although it worked fine as an S meter on RX and Ok for the plate voltage
and RF levels it turned out to be about 40% LESS sensitive than the
original. When I carefully checked the cathode resistors (5 Ohms)I
discovered that the meter was reading about that much too low!
Result Class A linear amplifier!!!!!
No wonder the anodes were getting hot!!!
Set things up properly by altering the multiplier resistor for the meter
from 3.3K to 2.2K and everything starts to run in AB1 as it should and I
get 80 Watts without red hot anodes!
However the overheating has definitely damaged my finals and I think
that they are a bit gassy as they Anode current on key down definitely
drifts upwards.
So next Junk sale I'll be looking for some more 6883B's as replacements,
fortunately as I explained they are quite common here in NZ.
Many thanks for all your suggestions, it just goes to show how easy it
is to miss the obvious even after more than 50 years in electronics.
Best 73's Cliff Wright ZL1BDA ex G3NIA.

On Tue, 28 Aug 2007 03:16:06 -0700,
wrote:

On 28 Ago, 11:59, (Geoffrey S. Mendelson) wrote:
wrote:
what exactly are "12 volt 6146B's" ?
6146B have 6.3V heater. What tube are you using exactly?

There were several variants with different heater voltages. I once
bought a bunch of them cheaply at a hamfest. If you were building
your own rig and could set the heater voltage, they were well worth
the price.


yes, I remember, but afair they had different "names", surely not
marked as 6146B.

6146W IIRC


73
Francesco IZ8DWF