Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
Regards Cliff Wright ZL1BDA ex G3NIA.

Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
=========================
Cliff , Does the TS-820 HV transformer have just 1 HV output or is there
also a lower voltage tapping.
I recall that the early Yaesu FT400/500 series (valve)transceivers had a
transformer with 600 and 850 V tappings.
The TV line sweep valves (tubes) in the PA worked well with the lower
voltage .....but 850V was toooo much especially when you used the PI
tank for matching the antenna (no external matching unit)
I used an old 1970 era FT-400 that way as my first TRX from 1985 - 1989.

Frank GM0CSZ / KN6WH

Highland Ham wrote:
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need
a bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?

=========================
Cliff , Does the TS-820 HV transformer have just 1 HV output or is there
also a lower voltage tapping.
I recall that the early Yaesu FT400/500 series (valve)transceivers had a
transformer with 600 and 850 V tappings.
The TV line sweep valves (tubes) in the PA worked well with the lower
voltage .....but 850V was toooo much especially when you used the PI
tank for matching the antenna (no external matching unit)
I used an old 1970 era FT-400 that way as my first TRX from 1985 - 1989.

Frank GM0CSZ / KN6WH
Hi Frank!
You know some years ago I had a similar Yaesu rig. I actually replaced
the sweep valves with 6146B's because of just the problem you describe.
When it was converted I had to pull all but one plate off the
neutralising cap beacause the interelectrode capacity of the "real"
TX valves was so much lower!!! Sold it when I got my more "advanced"
Kenwood a few years back.
However the 820S only has an 800 volt secondary with a bridge rectifier
and about 100 uF of smoothing caps.
I have discovered that valve testers are quite useless for testing
powerful tubes like 6146's and larger. They simply don't have a high
enough supply voltage built in and valves that test Ok can be a bit
"soft" and flashover at once with 1KV on the Anode.
However I hope to get some more 6146B's or their 12 volt version
the 6883B at a junk sale coming up soon. If not I'll look out for
another TT21 and modify the final box to take it.
At least then I'll be loafing along with 90 watts anode dissapation.
I have a "soft spot for the TT21 as I used a single one back in the 70's
to get DXCC and WAC. That worked with 1KV on the anode fine for years
and was dead stable!

One last point about Jap transceivers. They never seem to monitor grid
current. My home brew final did, and it was by far the best way to be
sure that your final was working properly in class AB1. In the 820s
there is even a spare switch wafer so I'm thinking of installing it
using the existing meter!
Regards
Cliff Wright ZL1BDA ex G3NIA.

On Sep 20, 7:38 am, cliff wright wrote:
Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.


Whoa, whoa. I know that tube ratings can be bent a little bit, and
while there is a tap on the transformer for "800V" this is intended to
be 750V to 800V after rectification, with load being drawn.

If you're measuring the voltage without load, you're right, it will be
higher than the voltage with load.

You might check that you're using the right tap on the input of the
transformer, too. IIRC there are 100V and 120V taps on the input.

I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!

See, if you're transmitting then you draw current and there's no
longer quite so HV there. 6146B's will stand up to a good amount of
abuse, and usually other components in the final compartment will arc
over and give up their smoke before the tubes.

I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.

Well, if you really want to, sure. But 6146B's served fine in these
radios for decades. Yeah, Kenwood pushed some of the numbers past a
strict reading of the tube limits but everyone pushed their 6146B's a
little past ICAS. (Remember, those were the days when Swan claimed to
get 600W out of a couple of sweep tubes.)

Tim.

Tim Shoppa wrote:
On Sep 20, 7:38 am, cliff wright wrote:

Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.



Whoa, whoa. I know that tube ratings can be bent a little bit, and
while there is a tap on the transformer for "800V" this is intended to
be 750V to 800V after rectification, with load being drawn.

If you're measuring the voltage without load, you're right, it will be
higher than the voltage with load.

You might check that you're using the right tap on the input of the
transformer, too. IIRC there are 100V and 120V taps on the input.


I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!


See, if you're transmitting then you draw current and there's no
longer quite so HV there. 6146B's will stand up to a good amount of
abuse, and usually other components in the final compartment will arc
over and give up their smoke before the tubes.


I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.


Well, if you really want to, sure. But 6146B's served fine in these
radios for decades. Yeah, Kenwood pushed some of the numbers past a
strict reading of the tube limits but everyone pushed their 6146B's a
little past ICAS. (Remember, those were the days when Swan claimed to
get 600W out of a couple of sweep tubes.)

Tim.

Well Tim OM.
Don't worry, I checked the voltage both on and off load. Since I've been
a ham for 50 years+ and a professional electronics engineer (now
retired) I'm pretty familiar with PSU regulation problems.
BTW the secondary is labelled 800 volts both on the transformer and in
the service manual, so there is no possibilty of error there.
With 60 mA of anode current for the 2 finals the voltage is 970 and
when putting out 75 watts (CW) it is still 890. (using 3 different meters)
However as you say it was made in a time of wishful thinking!!!!
Looked up an old ARRL handbook from the 70's while searching for ideas
and found a 4 sweep tube final allegedly putting out nearly 1KW.
However call me an old conservative (engineering wise anyway) but I
still like a factor of safety.
I'm off to a local junk sale in a couple of weeks and if I can get some
more 6146B's (or 12 volt equivalent) then I'll stock up and flog them to
death! But if I can get another TT21 (KT88 with a top cap anode) then
I'll drop down the tube bases, enlarge the chassis hole and replace the
6146's altogether.
As you probably know the TT21 has a 45 watt dissapation rating and can
be run safely up to 1.2KV in class AB1.
Then I can get the rated output without "blowing a gasket".
BTW what I said about a grid current meter is VERY important!!!
Nothing tells you if a class AB1 final is working properly as well.
In actual fact a pair of 6146B's would be VERY hard pressed to deliver
more than 130 watts ouput, even with an optimally designed final tank
circuit in AB1. Very few transcievers have such a good Pi network on all
bands either!
In conclusion I should point out that I mostly work CW on 14MHz, with
the odd excursion into SSB.

73's Cliff Wright ZL1BDA ex G3NIA

On Sep 20, 4:38 pm, cliff wright wrote:
Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
Regards Cliff Wright ZL1BDA ex G3NIA.

i'm considering to go for the same do u hav any ckt idea as well as
documents to create my own as of now i quiet new to this field dear
cliff wright.....

wrote:
On Sep 20, 4:38 pm, cliff wright wrote:

Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
Regards Cliff Wright ZL1BDA ex G3NIA.


i'm considering to go for the same do u hav any ckt idea as well as
documents to create my own as of now i quiet new to this field dear
cliff wright.....

Just an update for those who might be interested.
It turns out that my reservations about valve (tube) Testers were proved
to be correct.
I used a single 6883b in the final amp and got the following very
interesting results.
Tube 1 for a dc input of 84 watts the RF output was a miserable 25 watts
measured with a calibrated Marconi RF power meter.
Tube 2 for a Dc input of 63 watts the RF power was the same, vis 25 watts.
25 Watts is the maximum power rating of the Marconi test equipment.

So it is very obvious that damaged or low emission finals can have the
effect of drastically reducing the efficiency of the Power stage.
Fortunately I hope to source some more 6883B's or 6146B's this weekend.

So if your transmitter gets "feeble" but the Dc input remains the same
suspect your finals. Especially if it tends to red hot anodes!!!
&3's Cliff Wright ZL1BDA ex G3NIA.

wrote:
On Sep 20, 4:38 pm, cliff wright wrote:

Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
Regards Cliff Wright ZL1BDA ex G3NIA.


i'm considering to go for the same do u hav any ckt idea as well as
documents to create my own as of now i quiet new to this field dear
cliff wright.....

Just an update for those who might be interested.
It turns out that my reservations about valve (tube) Testers were proved
to be correct.
I used a single 6883b in the final amp and got the following very
interesting results.
Tube 1 for a dc input of 84 watts the RF output was a miserable 25 watts
measured with a calibrated Marconi RF power meter.
Tube 2 for a Dc input of 63 watts the RF power was the same, vis 25 watts.
25 Watts is the maximum power rating of the Marconi test equipment.

So it is very obvious that damaged or low emission finals can have the
effect of drastically reducing the efficiency of the Power stage.
Fortunately I hope to source some more 6883B's or 6146B's this weekend.

So if your transmitter gets "feeble" but the Dc input remains the same
suspect your finals. Especially if it tends to red hot anodes!!!
&3's Cliff Wright ZL1BDA ex G3NIA.

cliff wright wrote:
wrote:
On Sep 20, 4:38 pm, cliff wright wrote:

Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
Regards Cliff Wright ZL1BDA ex G3NIA.


i'm considering to go for the same do u hav any ckt idea as well as
documents to create my own as of now i quiet new to this field dear
cliff wright.....

Just an update for those who might be interested.
It turns out that my reservations about valve (tube) Testers were proved
to be correct.
I used a single 6883b in the final amp and got the following very
interesting results.
Tube 1 for a dc input of 84 watts the RF output was a miserable 25 watts
measured with a calibrated Marconi RF power meter.
Tube 2 for a Dc input of 63 watts the RF power was the same, vis 25 watts.
25 Watts is the maximum power rating of the Marconi test equipment.

So it is very obvious that damaged or low emission finals can have the
effect of drastically reducing the efficiency of the Power stage.
Fortunately I hope to source some more 6883B's or 6146B's this weekend.

So if your transmitter gets "feeble" but the Dc input remains the same
suspect your finals. Especially if it tends to red hot anodes!!!

Red hot anodes still doesn't sound right, Cliff. Did you have to turn
the bias pot to any unusual positions to get them to glow like that?

Weak emission tubes just don't draw much current, and even if I
cranked the bias current up to normal while their output would be
feeble I generally find their plates to be sucking current anemically
when they're low emission. Now, gassy tubes, especially if there is
enough grid current to upset the grid bias, that is a problem I've
been having with NOS tubes lately.

What's the grid voltage when you're done biasing? For my "good"
6146B's, it's almost always -50V in AB1. -75V or so is class C. If you
are setting the bias to something closer to -30V or -40V, I think
you're getting closer and closer to class A.

I remember spending a few weeks allowance on some known good 6146B's
when I was a kid. Are known good final tubes that hard to come by down
under? I'm starting to feel like I should send you some of mine just
to help you in your struggles :-). Besides, I'm mostly using 807's
here except for my Eico 720 these days!

Tim.

Tim Shoppa wrote:
cliff wright wrote:

wrote:

On Sep 20, 4:38 pm, cliff wright wrote:


Hi guys!
Am still going over the old TS-820 and found another problem re the
meter. It is important when replacing the meter to check the condition
of the multiplying resistors on the underchassis "HT" board and adjust
to suit the actual sensitivity of the meter.
Mine was reading 730 volts off load for final anode voltage but my
trusty old Avometer tells me that it was actually 1,040 volts.
Now this is WAY above the recommended anode voltage for even a 6146B
but since the tansformer secondary is 800 volts its probably correct.
I've now got the voltage reading correctly on the meter, but I'm now
very convinced that the reason for flashover in some 6146's is simply
excessive HT voltage. The finals are running in very dangerous
territory. Just a bit of SWR then Poof!!!
I'm now considering modifying the case and using a TT21 as a final.
These can stand the voltage with ease, are very easy to neutralise
and can give a good 65% efficiency in AB1 up to 30 Mhz. Will give me
around 80 watts out I reckon.
Just that my final box will be a bit taller and the old case will need a
bit of chopping about.
But then its an old rig and it might as well work properly, even
modified. Anyone elese tried major final tube changes in the Kenwood
hybrids?
Regards Cliff Wright ZL1BDA ex G3NIA.


i'm considering to go for the same do u hav any ckt idea as well as
documents to create my own as of now i quiet new to this field dear
cliff wright.....


Just an update for those who might be interested.
It turns out that my reservations about valve (tube) Testers were proved
to be correct.
I used a single 6883b in the final amp and got the following very
interesting results.
Tube 1 for a dc input of 84 watts the RF output was a miserable 25 watts
measured with a calibrated Marconi RF power meter.
Tube 2 for a Dc input of 63 watts the RF power was the same, vis 25 watts.
25 Watts is the maximum power rating of the Marconi test equipment.

So it is very obvious that damaged or low emission finals can have the
effect of drastically reducing the efficiency of the Power stage.
Fortunately I hope to source some more 6883B's or 6146B's this weekend.

So if your transmitter gets "feeble" but the Dc input remains the same
suspect your finals. Especially if it tends to red hot anodes!!!


Red hot anodes still doesn't sound right, Cliff. Did you have to turn
the bias pot to any unusual positions to get them to glow like that?

Weak emission tubes just don't draw much current, and even if I
cranked the bias current up to normal while their output would be
feeble I generally find their plates to be sucking current anemically
when they're low emission. Now, gassy tubes, especially if there is
enough grid current to upset the grid bias, that is a problem I've
been having with NOS tubes lately.

What's the grid voltage when you're done biasing? For my "good"
6146B's, it's almost always -50V in AB1. -75V or so is class C. If you
are setting the bias to something closer to -30V or -40V, I think
you're getting closer and closer to class A.

I remember spending a few weeks allowance on some known good 6146B's
when I was a kid. Are known good final tubes that hard to come by down
under? I'm starting to feel like I should send you some of mine just
to help you in your struggles :-). Besides, I'm mostly using 807's
here except for my Eico 720 these days!

Tim.


Hi Tim.
Yes the bias is correct as are all the other electrode voltages. I think
that you are correct in thinking that the tubes are no longer "Vacuum
Tubes" but more akin to 1920's soft types.
I'm pretty sure that the problem originally began with a loose ground
connection on the UHF antenna output cable.
This meant that the final was running into a terrible mismatch.
BTW over my 50 years+ as a Ham I've built several linear amps, including
ones using 811A's, 807's, 6146B's and even TT21's. I'm still of the
opinion that all these transceivers with class AB1 linears need a meter
position to measure grid current. In my experience the best way by far
to ensure proper operation in AB1 is to keep it from flowing!
As to relacements, well I hope to get some from a local "junk sale"
on Saturday next. The 6883B's have 12 volt heaters and were often used
in old local AM and SSB mobile radios by small ships and the forest
service. That means that there are quite a few around in NZ. Just as well!
The Kenwood is designed for a Japanese equivalent to the 6146B but a
simple mod to the heater wiring on the final PC board makes it possible
to use 6.3 volt or 12 volt heater tubes.
&#'s Cliff Wright ZL1BDA ex G3NIA