#31
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Quote:
The last chassis like that, I replaced to PT on, I replaced the 6X5, with a 5Y4, as the socket didn't have all the contacts for the more common 5Y3. If the transformer has a separate five volt winding for a rectifier tube, I prefer to use a five volt rectifier tube, fully knowing that the six volt rectifier tube isn't that reliable. |
#32
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The NOS one that went bad on me was a 6X5GT....
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#33
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There was a large difference. The 6X5 only draws 600ma, heater current@ 6.3 volts. I was tempted to use a 6AX5, but the heater current is 1.2 amps@ 6.3 amps. The Zenith power transformers were undersized, as it was, without adding to the load.
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#34
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The triode output versus the pentode has lower harmonic distortion but the plate efficiency is also much lower, reducing output power. Additionally, the handling of varying plate load, due to output transformer and speaker reactance across the frequency spectrum is improved with the triode. It is likely a tradeoff that Zenith accepted in exchange for better fidelity. This odd feature of the Zeniths is motivation enough to recap (and replace the tranny) and give it a serious listen.
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"When resistors increase in value, they're worthless" -Dave G |
#35
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Tube data sheets show the 6AC5 capable of 3-4 watts, with around 250 or so plate volts...-in SE..which your chassis is.
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Audiokarma |
#36
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I went to the workshop this morning and started early on my Zenith. I replaced a few small capacitors, and a 16 MFD 475 volt big capacitor. I checked almost all the tubes and put on a new power cord. I then proceed to "smoke test." So I yell "smoke test!" I powered it up slowly on an isolation transformer, and when I got up to about 50 volts, the current jumped way up. We concluded that the circuit is short.
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"If you wish to make an apple pie from scratch, you must first invent the universe." -Carl Sagan |
#37
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ok...at this point...you need ot see if the power tranny is shorted or not.
With the 6X5 rect out of the ckt and NO diodes in to sub it....( IOW--and OPEN ckt on the HV winding of the tranny), and ALL tubes out of the set...do another variac test. THIS time...you should NOT get much draw--no more than maybe 25 watts or so--likely less--with an open ckt on the transformer. If you DO--then disconnect ALL leads from it-other than the primary--and try again. If it STILL drews over 1 amp or higher--with no laod--the HV winding is shorted. if it then drops to a very low draw...there is SOMETHING still shorted i the ckt, likely a cap somewhere. |
#38
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I won't be able to work on this radio again for two weeks, the radio club will all be at the BirmingHAMfest on March 7, and so will I. So I should take all the tubes out and try it on the variac? I kind of suspected it was a capacitor, those darn things love to go short.
I got this ARRL The Radio Amateur's Handbook today while working on my Zenith. It goes into extreme detail on electrical theory of all types. There's some pretty brutal math in there.
__________________
"If you wish to make an apple pie from scratch, you must first invent the universe." -Carl Sagan Last edited by TUD1; 08-07-2016 at 10:21 PM. |
#39
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In the absence of my Zenith, my 1941 Philco is doing an A1 job. It sounds amazing and hasn't skipped a beat.
__________________
"If you wish to make an apple pie from scratch, you must first invent the universe." -Carl Sagan Last edited by TUD1; 08-07-2016 at 10:21 PM. |
#40
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The inside. It gets a little warm back there after a while.
__________________
"If you wish to make an apple pie from scratch, you must first invent the universe." -Carl Sagan Last edited by TUD1; 08-07-2016 at 10:21 PM. |
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