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Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
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Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
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In Reply to: Desperately seeking alignment help for Scott 370 (LT-111) posted by Dave Pogue on November 29, 2006 at 11:27:39:
Dave,If your tech can't align the RF section properly without instructions get another tech. He should use a good sweep generator for the IF's then tweak everything in mono for lowest harmonic distortion.
The multiplex section is another matter. I spent a load of time trying to get a supposedly "fully modded" 370 to work in stereo. Stereo signal had "birdies" which indicated that the internal multiplex oscillator wasn't locking onto the pilot signal.
MPX alignment instructions say to set the tuner for stereo: inject a pilot signal into the section, connect a scope to the junction of D501/502/503, short the secondary of T502(to disable the multiplex oscillator) and peak L501 and T501. Remove everything, put in a composite signal from the mpx generator with say 1khz audio on one channel and while viewing both audio outputs on a 2-channel scope, adjust T502 so the oscillator continues to "lock on" to the pilot signal while reducing the composite level as low as possible. Then put the bottom cover back on and adjust L-501,L-502, T501 and the separation pot for maximum separation (use the highest audio frequency available from the mpx generator). Should be able to get 30dB but I couldn't get much better than 25 up to 10kHz.
Even after this, I found that the birdies would come back after a few hours. Found that I had to increase the pilot injection level into the multiplex oscillator to maintain a better lock. Increased the value of one of the caps in the grid of V-501-A, may have been the 22pf (C526) - can't remember exactly.
Anyway the tuner worked fine - and SOUNDED great.
Finally, the 370 is a later version of the LT-110, redesigned to use Compactron tubes in a few places (to save money???). It has an extra IF stage and a slightly different mpx stage. Also for some "strange" reason, it has a 6X4 tube rectifier instead of solid state rectifiers.
The LT-110 also sounds VERY good - with better caps here and there.
Charles
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Follow Ups
- Scott 370 mpx alignment suggestions - stellavox 04:51:41 11/30/06 (1)
- I'll give your note to my tech ... - Dave Pogue 05:37:01 11/30/06 (0)
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