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Tuning meter string drops after about 30 seconds

T

Tomvette

Member
My 800 C tuning meter shows strong after warm up, about a 4 or so for about 30 seconds to a minute then drops to about 1.5 out of 5 segments.

Any thoughts on the cause of this? The sound of the tuner does not seem to change.
 
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Sounds more like one or more of the Tuner tubes is weak. If it's a fairly strong station you probably wouldn't notice any change. Swap the 6gk5 in V1 with the V9 6GK5. Checking to see if V1 is weak and the RF amp section(V1 and Front end inside the box) is ok with the other tube in it. V9 is the Stereo Beacon Amp. When you swap the V1 and V9 you may see some degradation in the stereo beacon lighting and automatic stereo function if the old V1 tube is weak/dying. 6GK5/6FQ5A is $5.00 @ abcvacuumtubes.com

The other tubes in the tuner section that are Rode hard and put away wet are V2 (6AQ8) and V3 (6HR6). V2 can be subbed with a 6DT8 for 1/5 the cost, as can V3 with a 6AH6 for about the same savings. V3 doesn't usually give away signal strength tho. V1-V2 are more likely to drop off strength. Spend $20 and get 2 of each. 6DT8's are $3.00ea and 6ah6/A are $3.00ea
While 6AQ8's and 6HR6 are $15.00ea There was a big run on 6HR6 and 6HS6 last year and a lot of places ran out of new old stock.
www.abcvacuumtubes.com
 
When I had problems with my tuning strength meter, to correct it I had to go through the process of adjusting the IF transformers. But my symptoms were slightly different than yours. My meter would register low on strong stations and stay low. I would go with Larry's suggestions first because they're easier and won't screw up your receiver if you make a mistake (and he knows WAY more than I do about these things).
 
larryderouin said:
Sounds more like one or more of the Tuner tubes is weak. If it's a fairly strong station you probably wouldn't notice any change. Swap the 6gk5 in V1 with the V9 6GK5. Checking to see if V1 is weak and the RF amp section(V1 and Front end inside the box) is ok with the other tube in it. V9 is the Stereo Beacon Amp. When you swap the V1 and V9 you may see some degradation in the stereo beacon lighting and automatic stereo function if the old V1 tube is weak/dying. 6GK5/6FQ5A is $5.00 @ abcvacuumtubes.com

The other tubes in the tuner section that are Rode hard and put away wet are V2 (6AQ8) and V3 (6HR6). V2 can be subbed with a 6DT8 for 1/5 the cost, as can V3 with a 6AH6 for about the same savings. V3 doesn't usually give away signal strength tho. V1-V2 are more likely to drop off strength. Spend $20 and get 2 of each. 6DT8's are $3.00ea and 6ah6/A are $3.00ea
While 6AQ8's and 6HR6 are $15.00ea There was a big run on 6HR6 and 6HS6 last year and a lot of places ran out of new old stock.
www.abcvacuumtubes.com
Click to expand...
Thank for the post. Several things corrected the issue but replacing V4, 6AU6 eliminated the drop in signal strength after 30 seconds or so.

You were spot on about the tubes. I had tested all of them with my EICO 667 Dynamic Mutual Conductance tester and the 6AU6 tested fine. That said I did not hold the test for 30 seconds! Anyway, many thanks for sharing your insights.
 
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