Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Fairbanks Morse Model 8a Problem
#1

Hi,

I've been working on this Model 8A..was dead, now playing, however I have too much voltage on both sides of the circuit for example...checking plate voltage on the 6k7's, 6l7, 5y3, 6c5, spec is 240v. I'll have 245v for about 5min then it jumps to 345v. In turn the voltage at pin4 of the 6k7's and 6l7 should be 105v and I have 155v(exactly 1/2 of the excess plate voltage. Bias voltage reacts the same 50v more.  All resistors & tubes check good but I'm replacing all resistors anyways. Have about 8 to go...The only oddity is no signal thru the antenna wire(if it's correct..wire goes to thru band selector switch to ground) and volume seems low until 50% after 70% it's a little distorted....If I hook an antenna lead up to the cap of the 6l7 or plate wire of the 6k7 reception is outstanding. Is there something obvious I am missing? Transformer is super cool, even after an hour. The only thing I have not checked is field coil resistance. Will do that tonight. All three bands are sensitive..can pick up more stations then my 38-116 hi fidelity.
 
Thanks in advance for any suggestions  

Bob  


Messages In This Thread
Fairbanks Morse Model 8a Problem - by bm071 - 01-15-2016, 09:23 AM
RE: Fairbanks Morse Model 8a Problem - by bm071 - 01-18-2016, 09:24 AM
RE: Fairbanks Morse Model 8a Problem - by bm071 - 01-18-2016, 09:40 AM
RE: Fairbanks Morse Model 8a Problem - by bm071 - 01-18-2016, 07:37 PM
RE: Fairbanks Morse Model 8a Problem - by bm071 - 01-20-2016, 09:19 AM
RE: Fairbanks Morse Model 8a Problem - by bm071 - 01-20-2016, 05:55 PM
RE: Fairbanks Morse Model 8a Problem - by bm071 - 01-20-2016, 05:59 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Correct model 84 Ac plug an cord type
From what I read Philco went to using brown rubber power cords in 1936, so cloth was used in the 1935 and earlier models...Arran — 11:25 PM
Correct model 84 Ac plug an cord type
Hi Bruce, I have not worked on an 84, but in general, power cords for almost any radio prior to 1938 was cloth covered...MrFixr55 — 08:34 PM
Restoring Philco 38-14
OK, well, so after staring at the sch again, I realized the problem had to be the #12/12A padder. I put a scope on the o...morzh — 08:15 PM
Correct model 84 Ac plug an cord type
Hello Bruce, I mostly use brown far as my cloth powercords go ! Here is the plug that I have used bakelite Acorn style...radiorich — 08:05 PM
Correct model 84 Ac plug an cord type
Looking for as correct as can find the right Ac plug an the correct colored cloth line. Ive seen many old photos but mos...Bruce — 04:13 PM
Restoring Philco 38-14
Rod Two Y-caps make sense if you use them from L/N to the chassis; this is only makes sense in the transformer radios...morzh — 10:11 AM
Restoring Philco 38-14
Mike, I'm curious about a specific use of he Y cap. Lately I've seen a single cap across the power transformer primary. ...RodB — 09:01 AM
Restoring Philco 38-14
hello morzh , That sounds like a plan ! Sincerely Richardradiorich — 07:45 AM
Restoring Philco 38-14
Richard, It helped some, but I still had the whining when engaging the rear power strip (I did not realize it was fro...morzh — 07:07 AM
Restoring Philco 38-14
Hello morzh, Yes , that dreaded hum in my room where i do alighment I have my cable modem and router plus desktop plus ...radiorich — 11:25 PM

[-]
Who's Online
There are currently no members online.

>