UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Reply
 
Thread Tools
Old 12th Apr 2020, 1:24 pm   #101
Devon60Ben
Tetrode
 
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 59
Default Re: Pilot U650

Thanks Turretslug,
Just been planning ahead to the IF and band alignment and located the adjustment points but have run into a serious problem that may be a showstopper.
The IF adjusters are fine but the band adjusters - C31 to C46 seem to have been butchered in the past so that many of the screw heads are damaged an unable to turn except 1 out of the 12. Currently I can't think of a potential solution!
Devon60Ben is offline   Reply With Quote
Old 26th Apr 2020, 7:43 am   #102
Devon60Ben
Tetrode
 
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 59
Default Re: Pilot U650

Finally the post arrived with a large 1500 ohm resistor to substitute for the field coil for testing purposes. The current Magnavox FC is 3200 ohms, std speaker was 1400 ohms.
With the resistor in place all plate voltages improved by 50V & Screens by around 20V so all much more in the ball park to the spec sheet.
Fitted a new output valve and the volume has now roughly doubled when on max and drawing less current with plate voltage increasing by 10V.
NOS magic eye arrived and looks great but doesn't open & close very much - staying around 3/4 open so need to look into that.
The "Kenable" PU Jack lead has also arrived so will test this out and report back.

So, should I be looking for a replacement speaker at around 1400 ohms? are there other options? Can the 3200 ohm remain? thanks
Devon60Ben is offline   Reply With Quote
Old 26th Apr 2020, 8:39 am   #103
Devon60Ben
Tetrode
 
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 59
Default Re: Pilot U650

Ipod now playing well through the pickup without anything in between at the moment - just switched to mono mode on the ipod. The speaker is poor but at least its all working.
Devon60Ben is offline   Reply With Quote
Old 26th Apr 2020, 10:03 am   #104
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 4,060
Default Re: Pilot U650

Quote:
Originally Posted by Devon60Ben View Post
NOS magic eye arrived and looks great but doesn't open & close very much - staying around 3/4 open so need to look into that.
The magic eye display depends on the AGC voltage swing on its grid. (Pin 5 of the 6U5G base and the plug to which it is connected). Unless there is a swing of several volts on the grid (up to 20 Volts AGC swing for the 6U5G), the eye display won't vary much, if at all. Easiest way to check the AGC voltage swing is to check the voltage with the set off tune, then again when tuned into a strong station. The thing that has most effect on signal strength (and hence AGC voltage), is of course the aerial.

This article, from the National Valve Museum site, originally from Radio Constructor March/April 1969, cites the 6U5G to explain how magic eyes work, so you might find it of interest:

http://www.r-type.org/articles/art-137.htm

As an aside, I restored a Pye 'Fenman 1' which sounded well enough at good volume on the internal wire aerial, but the EM80 magic eye didn't vary whether on or off tune. As EM80s are mercifully quite cheap, I took the easy option of fitting a new one, which made no difference. I made a little EM80 tester to vary the voltage on the grid to see how much it needed to go negative to vary the display. That proved that both the new and old eyes were working fine. It then dawned on me to plug in an external aerial, which gave a swing of several volts on the AGC line, and hence on the grid of the EM80. An interesting learning experience which cost me several hours of my life which I'll never get back!

Likewise, I restored a Unitra 'Figaro Special' which has a DM70 magic eye. (The 'exclamation mark' display). The set has an internal ferrite rod aerial on which it performs very well at good volume. However, the AGC varies little when off tune or tuned into a strong station. The set has an external aerial socket too, and when I plug an aerial into it, the AGC voltage swings by -9V and the display shrinks to just a dot.

Hope that might help a bit.
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now   Reply With Quote
Old 26th Apr 2020, 10:11 am   #105
Devon60Ben
Tetrode
 
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 59
Default Re: Pilot U650

Quote:
Originally Posted by David G4EBT View Post
Quote:
Originally Posted by Devon60Ben View Post
NOS magic eye arrived and looks great but doesn't open & close very much - staying around 3/4 open so need to look into that.
The magic eye display depends on the AGC voltage swing on its grid. (Pin 5 of the 6U5G base and the plug to which it is connected). Unless there is a swing of several volts on the grid (up to 20 Volts AGC swing for the 6U5G), the eye display won't vary much, if at all. Easiest way to check the AGC voltage swing is to check the voltage with the set off tune, then again when tuned into a strong station. The thing that has most effect on signal strength (and hence AGC voltage), is of course the aerial.
Thanks Very Much David,
This is how it looks currently.
Don't know anything about aerials yet - just have a coil of wire on the aerial feed and nothing on the earth.
Attached Thumbnails
Click image for larger version

Name:	Playing Ipod.jpg
Views:	16
Size:	70.1 KB
ID:	203995  
Devon60Ben is offline   Reply With Quote
Old 26th Apr 2020, 10:12 am   #106
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 14,354
Default Re: Pilot U650

Quote:
Originally Posted by Devon60Ben View Post

So, should I be looking for a replacement speaker at around 1400 ohms? are there other options? Can the 3200 ohm remain? thanks


Options would seem to be:


Stay with 3,200R if you're happy with the set's performance with this in place.


Look for a replacement aroiund 1,400R. Would be nearer to original.


Rewind the 3,200R speaker with slightly thicker magnet wire to reduce its resistance. Lot of effort and might not be as loud.



Leave the 1,500R resistor in place and fit a PM speaker. Might sound better but very non original though could be regarded as a typical "period" repair.



Polish it up and put it on a shelf secure in the knowledge that you could have restored it if you wanted to


It's really up to you at this stage......
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 6:33 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.