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

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

38-4 restoration need advice/ help
#1

Hi everyone, I am a new member with two 38-4 consoles. One is working fine with a recent recap (not by myself), and the other I have just recapped myself, and now have many questions so here goes... After replacing the paper tubulars and the elctrolytics, I reused the Mica caps, i tested socket voltages per bulletin #281, and noticed the DC readings were high. The power transformer is taller than my working set, and according to the part number stamped on it I have a 115v 25/40 hertz xfmr. Should I stop here and locate a 60hertz transformer? I do get recption on both bands, the volume level is low compared to the working set as well.
#2

25cy Transformer is ok. Sounds like you have other issues. Weak tubes or a bad resistor can give you those symptoms. Check voltages around the tubes to see where the problem is.
Terry
ps Where in MD?? Grew up in Sandy Spring.
#3

Tubes test OK on a heathkit TC2 ( not sure if thats a decent tester or not??) and play OK, in the working set. I have a order of resistors on the way from just radios, and I have to admit I only ohmed out about half of them when I did the caps. What tolerance should the resistors be within?
Also have a signal generator coming in the near future.

Terry, im down rt.108 in clarksville.
#4

Most older carbon resistors will have drifted way up in value or will behave strangely when under power. Nominal tolerence was 20% for most application. New ones with 5% or better toleranece are available for pennies apiece so it just makes sense to replace 'em all when doing a recap job. No foolproof to measure old resistors or capacitors.
#5

See if the voltage chart mentions anything about Ohms per volt with their readings. The resistors are worth checking even without taking voltage readings into account, especially on any resistor with a body end dot code.
Regards
Arran
#6

thanks, theres definatley some resistor problems, One which i tested last week is now open.... so ill dig in once they arrive. Anybody have preferrences on solder? I have some rosin core lead free, 96%tin, 4%silver. Is that OK?
#7

Lead-tin eutectic solder's the best. Rosin core is good. I don't like leadless solder.
#8

The resistors have arrived, ill dig back into it this week.
I also got the rubber isolators for the tuning cap. Anybody know how to get the two in the front into place? Can they be installed without taking the tuning cap off the chassis?
#9

Been busy lately, All new resistors and caps. I aligned it, tuning and reception is good on both bands, but I need some help, the volume is low, and it seems like there is too much bass.
I also have some high voltages. These problems were present before, I figured the off spec. components were to blame.
the DC tube socket voltages are around 20-30 volts high, at 115vac input.
heater voltages are ok. Any recommendations?

[Image: http://i818.photobucket.com/albums/zz105...ae2f7f.jpg]

[Image: http://i818.photobucket.com/albums/zz105...90451c.jpg]
#10

The DC tube voltages will be higher if you use today's Mains (120V vs 110V). You probably also use today's DMM and not the old type Voltmeter that would lower the voltage due to lower input impedance.

As for the volume low - Bass high,

1) Have you changed ALL capacitors and ALL resistors?
2) if not, start probing around the Switch #40 for all connected caps' and resistors' values.
3) If you haven't change #58/59 caps (likely to be micas not films) check them.
#11

Morzh, thanks,
I replaced all the resistors and all but the mica caps,
I used a variac to set input test voltage to the same voltage the schematic quoted for their readings (115v), line voltage just makes it worse.
Ill check over #40 with a meter, it does seem to work though.
#58-59 are new, Ill check them again.

Anything else???
#12

All parts 29-33 (caps-resistors). Especially 29.

Also....remote, but what if the output transformer is coming down with something?




Users browsing this thread:
[-]
Recent Posts
Philco 42-345 Restoration/Repair
Ok MrFixr55,  I have tried the DeoxIT D5 on the band switch and even though it has relieved the tension I felt when turn...osanders0311 — 11:11 AM
Part numbers to model cross
Is there a reference somewhere where you can punch in Philco part numbers and see what models those parts were used in?Jim Dutridge — 10:17 AM
Philco 42-345 Restoration/Repair
Hi OSanders, Look carefully at the band switch. Turn it slowly and "wiggle" it around the desired band. ...MrFixr55 — 12:33 AM
5U4 vs 5Z4 tubes
I think that RCA and GE introduced metal tubes in the USA in 1936.  I don't know if they were being made by RCA, GE or b...MrFixr55 — 11:20 PM
Philco 42-345 Restoration/Repair
Vlad95, Thank you for the stringing guides and wow there are so manyosanders0311 — 06:01 PM
5U4 vs 5Z4 tubes
A pre war Hallicrafters, and an early one too, very nice! 1936 is pretty early for metal tubes too, which would explain ...Arran — 05:58 PM
Philco 42-345 Restoration/Repair
Thanks Rod, "When you hear the background hiss and no station it usually indicates that the oscillator quit" ...osanders0311 — 05:52 PM
Philco 42-345 Restoration/Repair
RodB :beerchug:Vlad95 — 10:22 AM
Philco 42-345 Restoration/Repair
Vlad, you nailed it. Swiss and German roots.RodB — 09:54 AM
5U4 vs 5Z4 tubes
Well this is a Hallicrafters SX/9 circa 1936. No real issues so far although I dodged a real bullet with a cap that was...bridkarl — 07:59 AM

[-]
Who's Online
There are currently 1630 online users. [Complete List]
» 1 Member(s) | 1629 Guest(s)
Avatar

>