[NJARC] boat anchor question!

Tue, 13 May 2003 07:20:27 -0700 (PDT)

Thanks Al,

I went to check out your website. Super great crystal stuff. I learned more in 1/2 hour reading through your site than in many years!

I came across a fellow who makes some very nice crystal sets. In case anyone is interested... http://k8cix.tripod.com/crystalradio.html

I bought a really nice spark gap transmitter from him (picture is on his website) that was originally built by his father in 1917 (I have a picture of his father in his shack with the transmitter in the background). The transmitter is great fun to play with!

Any way. Thanks for the advise on the 342. As far as my tube tester goes, I don't know how to test IT! It has tested several 01A tubes successfully telling me good ones from bad ones. Also looking back at my notes on testing the tubes from the 342 tells me that two tubes test good, 5W4 (rectifier) and 6C5 RF oscillator.  Is it possible that the tube tester would function properly on these tubes, but improperly on say 6K7, 6L7, etc? 

I think I will probably "depart" with it.  anyone who may be interested, let me know. Would love to trade for something! Don't know what! Maybe a nice old vintage crystal set! Or something with a loose coupler!

Thanks
Eugene

Al Klase <[email protected]> wrote:
Hi Eugene,

Comments below:

Eugene Hertz wrote:
> Thanks Al for the advice..Yes, the 314 is awfully similar to the 342.
As for retubing, I'm not sure I follow your logic. If I 
replace the
caps now, won't I still need to replace all the tubes to see 
if the
recapping worked?

I'll bet a dollar to a donut that, if you retube the set it 
still won't play. Then what? The thing that kills tube is 
hours of operation, not years of age. few of these radios 
saw enough service to wear out the tubes. E.g., 24/7 
operation for about two years. This is a high performance 
radio, it will still play even wth a bunch of weak tubes.

I figured I would replace the tubes, then see what
did/didnt work. Unfortunately I dont have the time to do 
a recapping
job on this (or any other) radio! and as you know, this 
model is so
dense that it would require a major effort to do it. As for 
trying to
fix it, all I know is I powered it up, got no smoke and no 
audio
output. If course, no where in the manual TM could I find 
anything
about the proper impedence of a speaker, so I put an 8ohm 
one I had
lying around. Basically no sound, just dead.

Rated output impedance is 200 ohms. Look next to J3 on the 
right-hand side of the schematic. If the set's working 
you'll get sound out of an 8-ohm speaker. Sounds like a 
monumental mismatch, but it's really not that bad. A 
PA-system line-to-voice-coil transformer from Radio Shack 
will take care of things later on.

The little dial light
came on and the tube lit up (the only glass tube in it). 
So i decided
to check the tubes 'cause that was easy. I think 1 was good, 
one was
flat dead and the other 8 had "bad" in the tube tester 
(again, about 500 umhos).
While I have the floor, here let me ask a few basic 
electronic
questions!

1. What they hey is a uufd? (micro-micro farad?) is that
the same as a pf? (pico-farad)?

Roger that. A product of metric mania. 10E-12

2. What is the significance of a
micromho on my 177-B tube tester? I went to the trouble of 
getting this
because it was a mutual conductance, not just 
emissions...Yet, in the tube
test data booklet, it doesnt say what the manufacturer 
recommends for the
micromhos..so whats the value other than reading the red 
"bad" area and
green "good" area?

The settings of the tube tester account for different tubes 
having different transconductance (mutual conductance). Red 
and green's all you need to know unless you want to consult 
a tube manual. The fact that you found so many weak tubes 
suggests to me that you should test you tester with a known 
good tube. That thing's nearly 60 years old.

I made up a theory on what it means (so now you
fellows can correct it!) I imagined that anything less than 
1000 umho
(1mmho) would indicate the tube is attenuating and more than 
1000
means amplifying? How stupid is that notion? thanks! more 
questions
to come!When is the next

Meetings are the second friday of the month. Check the 
website if in doubt.

Al

> 
> 

-- 
Al Klase - N3FRQ
[email protected]
Flemington, NJ 08822
Web Page: http://www.webex.net/~skywaves/home.htm

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