Yesterday was alignment day kinda. I couldn’t get my scope working (operator I’m sure), been a long time since I used it. So I aligned with a fluke digital voltmeter. Pretty complicated procedure so its not something for a faint hearted person. I was pretty intimidated to begin with.
Anyway it sounds great with lots of bass notes in the audio. Am sure without the matching speaker it would not sound as good.
Got a couple small projects to clean up next, then, back to the sx28a.
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| 2011-04-03 |
“Minnie sings”. One happy “old man” here. Yesterday, All of the resistance measurements were taken, and a few (4) problems were fixed. All of the tubes were checked and 2 weak ones replaced. At some point in time, whomever worked on it last switched 2 tubes (old style with “grid caps”. Amazingly, both of those tubes tested OK.
Today, all of the voltage reading were taken from each tube pin, and only a couple were out of limits, which had an easy remedy.
This afternoon, I hooked the original speaker (compliments of KI7PG) to it and applied power. To my surprise good strong signal were heard on the AM broadcast band. Trying the other HF bands I receive signals on all on just a short piece of wire for an antenna.
Tomorrows (I hope) project will be to fix the inoperable s-meter. I have a spare just in case. Then to the next big step, an alignment.
Shown below is “Minnie” singing loud and clear a “foreign broadcast” on 18 mc. A Portuguese station probably in S. America.
Hooray. !!!! A sigh of relief. Minnie sings. The capacitor replacement was finished this PM. Needless to say, I could not wait to find out if the power transformer was good. After a bit of “nervous anticipation” I hooked a cheap 8 ohm speaker to the phone jack, a 10 foot piece of wire for an antenna, and plugged it in. After about 30 seconds, some beautiful noises began from the speaker.
The “AF” gain control was very scratchy, but a bit of “deoxit” has taken care of that. The “S” meter does not appear to function at this point, but, it should not be a serious problem. All of the other controls appear to function normally.
The sensitivity of “Minnie” is amazing. I am copying more AM stations than I have heard in years.
Next step will be to back up a bit and check all the resistance meas. from each tube pin, and then all the voltages. Then, an alignment with the oscilloscope (big job).
“Minnie” should sound lots better with the proper 5k impedance speaker hooked up.
(more to come)
Back to work on “Minnie” after a few days in the sunshine in Arizona visiting with my daughter and son in law, and spending a day with an old friend N7VF whom I met in Alaska in 1965 and hadn’t seen in 35 years. Great trip.
Also picked up a signal generator at a great price while there and had it shipped home.
And, picked my first fresh orange while there.
Today was spent at the Mike&Key club hamfest in Puyallup, WA. It was very crowded, but got to see lots of old friends and meet some new ones.
It was a special day because a very good friend, KI7PG, presented me with a PM23 speaker (matching the SX28) which belonged to his father W7GIP (sk). It is in perfect shape with the factory inspection tag attached dated Feb. 1940. Inside was his fathers QSL card, which will remain with the speaker forever. I promised him he could tune “Minnie” to his hearts content when she begins to sing.
Patrice told me today she was having trouble understanding which radio I was working on, since there is 2 projects going on at the same time. One is the SX 28A & the other is SX 28. I think after today there will be a new category for the 28.
Since it has been too cold in the shop to spend a lot of time out there, I decided to bring the SX 28 into the “shack” where it is warm. The band indicator & bandspread have now been restrung, the front panel removed & cleaned & meters bezels also. Upon removing the front panel I found that someone on the assembly line in 1943 had put their initials “MN” in white paint on a back corner where it has been covered up all these years.
Upon finding them, I told Patrice that I had found the initials “MN”, and that they probably stood for “Minnie Nelson”. So-oo, now she can distinguish between radios. The SX 28 has now become “Minnie”. Problem solved.
“Minnie” is now all reassembled and looking pretty. (hope she sounds as good as she looks)
Lots of progress today, so as soon as more “caps” arrive, I can finish that replacement project and begin resistance testing & then apply power and check for voltages.