No plate dip on TS-820
 

When trying to tune the final amp on my Kenwood TS-820, I get little or no
plate dip.
The amp can be tuned though, but I only get 50 W HF out, instead of 100 W.
Plate current is nominal at 250 mA and 800 V on the 6146B anodes.

I made these measurements with the rig connected to a 50 ohms dummy load
and the HF output was confirmed with a HP 432A power mwter.

So I get 50 W HF out for 200 W DC in. Efficiency is terrible at only 25%.
All the missing HF power must be dissipated in the anodes because they glow
red after a few seconds.

The same thing happens on all bands. Sometimes, when trying to tune on 7
MHz, plate current gets higher than 350 mA and the rig fuse blows.

I suspect there must be something wrong in the tank circuit.

Upon visual inspection, nothing looks charred in there. No arcing noises.

I checked the plate capacitor, which is OK. I unsoldered it and measured it
@ .001 uF, as it should be.

So I am wondering where to look next. Any ideas?

many tnx in advance

Angel Vilaseca HB9SLV

One of your 6146B tubes may be gassy. Remove one tube completely
(don't just lift the plate connector), key the rig with no drive
and check that you have 20mA plate current with the remaining tube.
Add drive, tune and load for 125mA with the single tube,
and see if you still get 50W output. Repeat tests with other tube.

If the tubes are balanced, each will draw 20mA quiescent current
with the same setting of final bias adjustment.

73,
Ed Knobloch K4PF

Angel Vilaseca wrote:
When trying to tune the final amp on my Kenwood TS-820, I get little or no
plate dip.
The amp can be tuned though, but I only get 50 W HF out, instead of 100 W.
Plate current is nominal at 250 mA and 800 V on the 6146B anodes.

I made these measurements with the rig connected to a 50 ohms dummy load
and the HF output was confirmed with a HP 432A power mwter.

So I get 50 W HF out for 200 W DC in. Efficiency is terrible at only 25%.
All the missing HF power must be dissipated in the anodes because they glow
red after a few seconds.

The same thing happens on all bands. Sometimes, when trying to tune on 7
MHz, plate current gets higher than 350 mA and the rig fuse blows.

I suspect there must be something wrong in the tank circuit.

Upon visual inspection, nothing looks charred in there. No arcing noises.

I checked the plate capacitor, which is OK. I unsoldered it and measured it
@ .001 uF, as it should be.

So I am wondering where to look next. Any ideas?

many tnx in advance

Angel Vilaseca HB9SLV

Sounds like you have the plate loading capacitor set to high (not
enough capacitance). Try turning it so it is fully closed and then see
if you get a proper plate current dip.

73
Gary K4FMX


On 30 Jan 2004 06:51:49 GMT, Angel Vilaseca
wrote:

When trying to tune the final amp on my Kenwood TS-820, I get little or no
plate dip.
The amp can be tuned though, but I only get 50 W HF out, instead of 100 W.
Plate current is nominal at 250 mA and 800 V on the 6146B anodes.

I made these measurements with the rig connected to a 50 ohms dummy load
and the HF output was confirmed with a HP 432A power mwter.

So I get 50 W HF out for 200 W DC in. Efficiency is terrible at only 25%.
All the missing HF power must be dissipated in the anodes because they glow
red after a few seconds.

The same thing happens on all bands. Sometimes, when trying to tune on 7
MHz, plate current gets higher than 350 mA and the rig fuse blows.

I suspect there must be something wrong in the tank circuit.

Upon visual inspection, nothing looks charred in there. No arcing noises.

I checked the plate capacitor, which is OK. I unsoldered it and measured it
@ .001 uF, as it should be.

So I am wondering where to look next. Any ideas?

many tnx in advance

Angel Vilaseca HB9SLV

Hmmmmm... Les see... I don't know this rig, but...

No dip.

You say: "The amp can be tuned though, but I only get 50 W HF out..."

I don't know what "tuned through" means Do tell. Is there any kind of a
PEAK in the output power when tuning either the plate tuning or the plate
loading?

Not sure where to go from here, but these two controls, when not behaving
normally, indicate that either there is not a tank circuit (something is
shorted or open). This could be something in the tank ckt OR the tube.

Getting 50 watts seems to indicate that the plate circuit is NEAR resonance,
so something must be close to right. I'd look @ tube voltages (Be careful)

Ran out of ideas.

73,
--
Steve N, K,9;d, c. i My email has no u's.


"Angel Vilaseca" wrote in message
...
When trying to tune the final amp on my Kenwood TS-820, I get little or no
plate dip.
The amp can be tuned though, but I only get 50 W HF out, instead of 100 W.
Plate current is nominal at 250 mA and 800 V on the 6146B anodes.

I made these measurements with the rig connected to a 50 ohms dummy load
and the HF output was confirmed with a HP 432A power mwter.

So I get 50 W HF out for 200 W DC in. Efficiency is terrible at only 25%.
All the missing HF power must be dissipated in the anodes because they
glow
red after a few seconds.

The same thing happens on all bands. Sometimes, when trying to tune on 7
MHz, plate current gets higher than 350 mA and the rig fuse blows.

I suspect there must be something wrong in the tank circuit.

Upon visual inspection, nothing looks charred in there. No arcing noises.

I checked the plate capacitor, which is OK. I unsoldered it and measured
it
@ .001 uF, as it should be.

So I am wondering where to look next. Any ideas?

many tnx in advance

Angel Vilaseca HB9SLV

"Steve Nosko"
wrote

Hmmmmm... Les see... I don't know this rig, but...

No dip.

You say: "The amp can be tuned though, but I only get 50 W HF out..."

I don't know what "tuned through" means Do tell.

***** Through has a different spelling and meaning to "though",let's
ask the OP what he meant!

Brian Goldsmith.

"Steve Nosko" wrote in
:

Hmmmmm... Les see... I don't know this rig, but...

No dip.

You say: "The amp can be tuned though, but I only get 50 W HF out..."

I don't know what "tuned through" means Do tell. Is there any
kind of a PEAK in the output power when tuning either the plate tuning
or the plate loading?

Not sure where to go from here, but these two controls, when not
behaving normally, indicate that either there is not a tank circuit
(something is shorted or open). This could be something in the tank
ckt OR the tube.

Getting 50 watts seems to indicate that the plate circuit is NEAR
resonance, so something must be close to right. I'd look @ tube
voltages (Be careful)

Ran out of ideas.

73,

Hi,

tnx for your answer.

I can obtain a very shallow dip in plate current when first tuning at low
power (there is a TUN switch on the TS 820). After that , the instructions
manual indicates to switch to CW mode, switch to xmit and quickly adjust
the plate and load caps while watching the RF out dial. Tune to max power
out. That is when I can get 50 Watts out, with the plate control about
where it should be as per the numbers printed on the dial and the load cap
at about mid-range. Both controls peak quite well.

However, the problem is that there should be twice this power output.
Furthermore, after about 10 seconds, the plates of the 6146Bs start to glow
red. So I guess that all the missing power output is indeed being
generated, but ends up heating the plates.

All of this happens when operating on 20 meters, my favorite band. When
trying to tune on 40 meters, things are much worse.
What has happened a couple of times is that when alternately adjusting the
plate and load caps, they don't actually peak. Instead, I can obtain a
higher and higher power output and higher and higher plate current, until
the rig fuse blows after a few seconds. There must be an oscillation in the
final stage. I will re-check neutralization.

Voltages on the tubes are OK: -60 V on the grids, +247 V on the screens,
+800 V on the plates on SSB, without modulation.

Vy 73 de HB9SLV

Ray di Tutto wrote in message . ..
"Steve Nosko" wrote in
:

Hmmmmm... Les see... I don't know this rig, but...

No dip.

You say: "The amp can be tuned though, but I only get 50 W HF out..."

I don't know what "tuned through" means Do tell. Is there any
kind of a PEAK in the output power when tuning either the plate tuning
or the plate loading?

Not sure where to go from here, but these two controls, when not
behaving normally, indicate that either there is not a tank circuit
(something is shorted or open). This could be something in the tank
ckt OR the tube.

Getting 50 watts seems to indicate that the plate circuit is NEAR
resonance, so something must be close to right. I'd look @ tube
voltages (Be careful)

Ran out of ideas.

73,

Hi,

tnx for your answer.

I can obtain a very shallow dip in plate current when first tuning at low
power (there is a TUN switch on the TS 820). After that , the instructions
manual indicates to switch to CW mode, switch to xmit and quickly adjust
the plate and load caps while watching the RF out dial. Tune to max power
out. That is when I can get 50 Watts out, with the plate control about
where it should be as per the numbers printed on the dial and the load cap
at about mid-range. Both controls peak quite well.

However, the problem is that there should be twice this power output.
Furthermore, after about 10 seconds, the plates of the 6146Bs start to glow
red. So I guess that all the missing power output is indeed being
generated, but ends up heating the plates.

All of this happens when operating on 20 meters, my favorite band. When
trying to tune on 40 meters, things are much worse.
What has happened a couple of times is that when alternately adjusting the
plate and load caps, they don't actually peak. Instead, I can obtain a
higher and higher power output and higher and higher plate current, until
the rig fuse blows after a few seconds. There must be an oscillation in the
final stage. I will re-check neutralization.

Voltages on the tubes are OK: -60 V on the grids, +247 V on the screens,
+800 V on the plates on SSB, without modulation.

Vy 73 de HB9SLV
I figure the shaft is slipping on the load control and the load
cap is locked in full load position,(min capacity)..you would not see
a dip on any band and output would be low.Kenwood shaft couplings are
plastic,they crack and become loose..W4PQW

On 01 Feb 2004 07:05:17 GMT, Ray di Tutto wrote:

"Steve Nosko" wrote in
:

Hmmmmm... Les see... I don't know this rig, but...

No dip.

You say: "The amp can be tuned though, but I only get 50 W HF out..."

I don't know what "tuned through" means Do tell. Is there any
kind of a PEAK in the output power when tuning either the plate tuning
or the plate loading?

Not sure where to go from here, but these two controls, when not
behaving normally, indicate that either there is not a tank circuit
(something is shorted or open). This could be something in the tank
ckt OR the tube.

Getting 50 watts seems to indicate that the plate circuit is NEAR
resonance, so something must be close to right. I'd look @ tube
voltages (Be careful)

Ran out of ideas.

73,

Hi,

tnx for your answer.

I can obtain a very shallow dip in plate current when first tuning at low
power (there is a TUN switch on the TS 820). After that , the instructions
manual indicates to switch to CW mode, switch to xmit and quickly adjust
the plate and load caps while watching the RF out dial. Tune to max power
out. That is when I can get 50 Watts out, with the plate control about
where it should be as per the numbers printed on the dial and the load cap
at about mid-range. Both controls peak quite well.

However, the problem is that there should be twice this power output.
Furthermore, after about 10 seconds, the plates of the 6146Bs start to glow
red. So I guess that all the missing power output is indeed being
generated, but ends up heating the plates.

All of this happens when operating on 20 meters, my favorite band. When
trying to tune on 40 meters, things are much worse.
What has happened a couple of times is that when alternately adjusting the
plate and load caps, they don't actually peak. Instead, I can obtain a
higher and higher power output and higher and higher plate current, until
the rig fuse blows after a few seconds. There must be an oscillation in the
final stage. I will re-check neutralization.

Voltages on the tubes are OK: -60 V on the grids, +247 V on the screens,
+800 V on the plates on SSB, without modulation.

Vy 73 de HB9SLV

Have you tried the basic stuff first, like installing a new pair of
final tubes?

How much plate current are you using, at maxium?
at minimum dip?

Is the antenna within the proper impendance range?
Tried tuning up using a dummy load?

Did this problem happen suddenly?

Doug

Wasn't there a switch on the back of some early Kenwoods for nuetralizing
and ( hazily) some kind of bias adhustment ???
Maybe Check the manual for these
--
73- Cambio - Keyboard To You (:-)

If one of the finals is "open", it will change the circuit impedence and might
be a contributing factor.