No plate dip on Kenwood TS 820

[Ray di Tutto]

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

 

[Sofie]

Ray di Tutto:
Replace the 6146 final tube..... and re-neutralize to eliminate spurious
parasitic oscillations.
Be very brief with you "key down" tune up time or damage to the final tube
will result.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
----------------------------


"Ray di Tutto" <ray@o-matic.com> wrote in message
news:Xns9480526373172rayomaticcom@212.35.34.213...

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

 

[Stephen Weidner]

I had the plate choke short (no visible signs of damage) that caused the
same problem. Rewound it with the same size
wire, coated it with Q-DOPE and it worked perfect.

73,
Steve, WB7WHF

"Sofie" <sofie@olypen.com> wrote in message
news:101ktu2ebu4u79c@corp.supernews.com...

Ray di Tutto:
Replace the 6146 final tube..... and re-neutralize to eliminate spurious
parasitic oscillations.
Be very brief with you "key down" tune up time or damage to the final tube
will result.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
----------------------------


"Ray di Tutto" <ray@o-matic.com> wrote in message
news:Xns9480526373172rayomaticcom@212.35.34.213...
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