Amplifier R-4359A

[TCW]

Hello,

I have an Amplifier R-4359A in my TI-1. It sounds like the singer is singing through a tube. The base seems weak. I adjusted the treble and base and this gave a minor improvement.  I checked wiring as shown in 2-6. Any ideas of first steps.

Tom

[Ron Rich]

Hi Tom,
Since this phono is new to you, I suggest you start with the needle-- is that any good/correct ?-is the pressure correct ? Ron Rich

[TCW]

Ron,

I forgot to mention I replaced it last week. 4.31 grams. Further improvement was achieved. - Tom

[Ron Rich]

Tom,
You "replaced it"-- did you check the needle pressure BEFORE replacing it ? Did you replace it with an aftermarket sub., or an OEM needle ? Ron Rich

[TCW]

OEM, N44-7. 4.1 grams before and 4.31 after

[Ron Rich]

L@@ks as if you got that base covered-- amp rebuild --- Ron Rich

[TCW]

Ron,

I got a B&K Model 707 Dyna Jet Dynamic Mutual Conductance tester. I'll need to make sure its calibrated and then check all these tubes out. Do you think this could be caused by weak power tubes AKA 7868. Or maybe an under performing rectifier tube?

Tom

[Ron Rich]

Tom,
Remember the old saying-- a chain is only as strong as it's weakest link---Ron Rich

[TCW]

Update,

I didn't bother to calibrate the 707 and went ahead and began testing the 7868's. The first three rang in at 78%. The third one moved to 76% and then dropped quickly to 22%. I would imagine that this condition would make one channel under perform but my sound issue effected both. 5U4GB rectifier tested weak 22%. Disclaimer is that my 707 is set up to test 5U4 tubes so I used this setting to check my 5U4GB. They are wired exactly same but different ratings or performance. I found the spec sheet 5U4-G, 5U4-GA, 5U4-GB here (https://tdsl.duncanamps.com/pdf/dragos.pdf), but no 5U4. The 12AX7's tested 16% & 12%. I'm going to have to buy a fortune in tubes.

[Ken Layton]

One thing I found in the Rowe amplifiers using 7868 tubes, is off value (out of tolerance) resistors in the 7868 output circuits. It's been 30 years since I last saw one of those amplifiers.

[Ron Rich]

Guyz,
That's very common in all jukebox amps -- regardless of the output tube number. Ron Rich

[mauro]

I would trust that tube tester, the 707 holds its calibration very well and the results you gave make sense. On the 707 and most tube testers a 5U4 is tested the same, no matter what letters follow it. Just read carefully as sometimes the manual will state "good tube if over 22" or similar.