Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12, 2025) x

Thread Closed

38-5 poor signal to noise ratio
#6

Thank you all for the info and ideas in your replies, I welcome any further comments and observations on what I ask or state below:

Steve, thanks for leading me to deeper antenna research. I have a (little) better understanding of loop antennas now, how/why they work. I don’t really have a convenient spot/room in close proximity to the radio to set up a DIY loop antenna, so maybe I try another idea I found on the web: a grounded ~50 foot length of wire with six 6” turns near the end in close proximity to the radio? It’s ok to just lay (anchor if/as necessary) the wire out across my roof if I don’t have good a way to string it up?

New to this, I don’t yet understand why these antenna ideas are just in close proximity to the radio rather than connected to the antenna terminal of the radio??

Ed, I have done some searching for RFI sources, no luck yet, will keep trying. Hmmm… although wifi is at a MUCH higher frequency, I wonder if the base station/access point hardware in the home might generate other electronic noise within “x” proximity? AC/DC power supplies?

Rod, thanks for that A/B, reinforcing what I hoped would be a simple troubleshooting tree for that. 

Mike, it is unrestored, yet in immaculate condition. So far I believe the only components ever replaced are the 18uf cap can & the 6A8G tube, and now the AC cord. All other parts are Philco, though I haven’t pulled all the tube covers yet, didn’t want to add any variables to my first operation on her. The cap and tube replacement were probably done before the early ‘60s, maybe even a decade or more earlier. Soooo… even though the radio behaves well, no nasty buzz like the 1939 Gibson EH 185 amp, I better start with the three electrolytic cap cans, 8+10uf dual, 16uf & 18uf.

I don’t think I can get those values in cosmetically correct cans, so what do radio restorers do, replace with modern cans, or abandon the existing cans cosmetically in place and try to find room for physically smaller caps in the underside of the chassis?

Just sharing, any of my vintage gear that hasn’t been played in more than 6 months to a year or so, I bring up slowly with a variac using a cap reforming “recipe” I learned from the recently late Bob Rissi of Risson Amplifiers: 25Vac for 5 minutes, 10Vac increase every 2 minutes up to operating voltage. I don’t know that i’ve ever saved or truly reformed any old caps, but I do it just in case it helps. If it is a repair job, I add an amp meter in front of the variac to help avoid surprises.

I’m going to investigate that procedure deeper on the EH 185 next time by measuring the B+ off the rectifier while the AC is ramped up. When I fired up the EH 185 the first time, it didn’t draw any current or make a hum until was up to 85Vac for about 90 seconds - then it just all of a sudden came alive with a loud nasty buzz. So I think at low voltages the 5U4 cathode doesn't get hot enough to generate the electron field used for the tube to operate --- therefore, no rectification and no high voltage. So I suspect the “Slow Cap Reforming" process up to that point really wasn’t useful, as the caps weren't getting any voltage! New procedure would be to bring up the AC until the rectifier produces DC and start the 5 minutes there, figure out the 2 minute increments from that point.

Thanks again, sorry, didn’t mean to go on so long!


Messages In This Thread
38-5 poor signal to noise ratio - by Rootboy - 04-12-2020, 11:14 PM
RE: 38-5 poor signal to noise ratio - by RodB - 04-13-2020, 10:55 AM
RE: 38-5 poor signal to noise ratio - by morzh - 04-13-2020, 11:08 AM
RE: 38-5 poor signal to noise ratio - by Rootboy - 04-13-2020, 07:15 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
54C Complete Teardown/Rebuild
Hello Roy, here is this one sincerely Richardradiorich — 12:45 AM
54C Complete Teardown/Rebuild
Richard, Had grabbed it already but thank you just the same.  I find myself wanting to find some way to block out the...glyphmon — 12:03 AM
54C Complete Teardown/Rebuild
Hello roy, here is a link to the schematic . Sincerely Richardradiorich — 11:54 PM
54C Complete Teardown/Rebuild
Richard, The Silvertone 2014 also is a transformerless set, so I am incorporating a 1:1 600 ohm audio isolation transfo...glyphmon — 11:37 PM
Preliminary work on wife's Silvertone 2014
Did an alignment today which was interesting.  IF alignment went great, almost all was already spot-on.  Adjusting on th...glyphmon — 11:35 PM
54C Complete Teardown/Rebuild
The main problem with adding a Bluetooth input is that this set lacks a traditional power transformer to isolate it from...radiorich — 11:19 PM
54C Cabinet Refinish
I started stripping this cabinet before it got super chilly out because I knew I wasn't going to be able to work on ...glyphmon — 11:18 PM
54C Complete Teardown/Rebuild
While I'm waiting to wrap up the final steps on my wife's Silvertone 2014, I started disassembly on the next project.  O...glyphmon — 11:07 PM
Preliminary work on wife's Silvertone 2014
Hello roy, that great news glad it worked out for you !! Sincerely Richardradiorich — 10:50 PM
Preliminary work on wife's Silvertone 2014
Safety caps arrived today.  Soldered one in and had a successful first power-up.  No magic smoke escaped and it tunes in...glyphmon — 09:53 PM

[-]
Who's Online
There are currently 1565 online users. [Complete List]
» 1 Member(s) | 1564 Guest(s)
Avatar

>