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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Closed Thread
 
Thread Tools
Old 11th Feb 2013, 12:44 pm   #1
HQsignals
Retired Dormant Member
 
Join Date: Feb 2013
Location: East Flanders - Belgium
Posts: 8
Default Paraset replica regen problem.

Hi all,

Although I'm still quite new to valve radios, I've been building a Paraset replica.
My problem with the receiver section is that the regen doesn't work or at least doesn't work properly.

The regen doesn't work, but after a few taps on the grid of the regen 6SK7, sometimes I can get the regen to work. But then it works with a high pitch noise in the audio and when I bump out of regeneration, the regen doesn't start anymore. Thus I have to tap the grid a few times again, to get it to work.

Even when it regenerates, I get audio at the anode but not at the anode of the second stage, which is the audio amp. (Seems like this causes a heavier load on the regen).
http://www.google.be/imgres?imgurl=h...ed=0CDMQ9QEwAQ

I think it might have something to do with bad feedback, but I'd like to hear a second opinion. I've had the same problem with another regen I made, so I think it might be something important to know.

Cheers!
HQsignals is offline  
Old 11th Feb 2013, 3:25 pm   #2
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: Paraset replica regen problem.

Try a new (or at least known-good) valve? It's not unknown for welded/soldered connections in them to fail.
G6Tanuki is offline  
Old 12th Feb 2013, 10:21 am   #3
HQsignals
Retired Dormant Member
 
Join Date: Feb 2013
Location: East Flanders - Belgium
Posts: 8
Default Re: Paraset replica regen problem.

Tried swapping valves yesterday, but it didn't change anything although I was able to hear faint audio at the output of the audio amp stage. So I believe the detector is working, but the feedback for the regen is not working properly. Think I might have a look at the regen coil.
HQsignals is offline  
Old 15th Feb 2013, 11:40 pm   #4
peter.sables
Rest in Peace
 
peter.sables's Avatar
 
Join Date: Dec 2007
Location: Doncaster, South Yorkshire, UK.
Posts: 385
Default Re: Paraset replica regen problem.

hi

Try 2 extra turns on the feed back coil.

pete
peter.sables is offline  
Old 15th Feb 2013, 11:49 pm   #5
Anthony Thomas
Hexode
 
Join Date: Jan 2013
Location: Ă…lesund, Norway
Posts: 361
Default Re: Paraset replica regen problem.

Is the polarity of the feedback coil correct?
Anthony Thomas is offline  
Old 21st Mar 2015, 9:10 pm   #6
HQsignals
Retired Dormant Member
 
Join Date: Feb 2013
Location: East Flanders - Belgium
Posts: 8
Default Re: Paraset replica regen problem.

Hi all,

has been a while since I've found time to look at this set(and this topic).
Yesterday I had a look at the paraset receiver with an oscilloscope,and noticed the following:

the output 'noise' I hear is a quite clean signal of around 10kHz,which comes from the regenerative detector,straight through towards the output amplifier,into the headphones.When I go out of regeneration by setting the feedback knob to zero,nothing happens.If I then increase feedback,the regeneration kicks in quite suddenly,but always at the same point of feedback.When this happens,a nearly pure 10kHz signal of a few volts in amplitude can be seen on the scope.The amplitude of this signal can be varied with the regeneration knob,but the frequency remains almost unchanged (max a few hundreds of Hz difference).So no regeneration = no signal of 10kHz. and when there is regeneration,the reaction knob allows me to change the amplitude of this 10kHz signal.

when I unplug the headphones,and go to the point where regeneration kicks in,the signal is not nearly as large (only a few tens of mV's).I believe this is because of the amplification of the second stage and the headphones impedance.

winding directions are ok,but coupling might be a bit tight.have checked this,but this is not the source of the 10kHz 'noise',only the kicking in of the regeneration.

So I am still wondering what might cause this 10kHz signal. I've been reading about the self quenching regenerative receivers,which seem to work in a similar way.Could it have something to do with that?

kind regards,
Bjorn
HQsignals is offline  
Old 26th Mar 2015, 2:04 pm   #7
AlanC
Hexode
 
AlanC's Avatar
 
Join Date: Jul 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 312
Default Re: Paraset replica regen problem.

Well oscillators (and regenerative detectors when oscillating) can 'squeg' which is where the oscillation builds up a negative charge on the valve grid, causing it to cut off (quench) until the charge leaks away, when the cycle repeats. It might be that this is what is happening, the 10khz being the 'quench' frequency.

In a regenerative receiver, it can happen if the reaction is wound up too much, or if the supply decoupling is poor, or the grid leak and coupling capacitor, between them, have too long a time constant. It may actually be that the stage is working properly, and you are provoking it into squegging rather than pure RF oscillation by poking the grid!

But it sounds to me like the audio stage isn't working, and a good plan might be to fix that and then re-evaluate the situation. You should have high voltage on pins 8 and 6 of the audio 6SK7, around 3 to 6 volts or something like that on pin 5, and 0 volts on pin 3 and 4. Touching pin 4 should produce a hum or buzz from the headphones.

Hope this helps,
Alan
__________________
Always expect the unexpected...
AlanC is offline  
Old 28th Mar 2015, 7:51 pm   #8
HQsignals
Retired Dormant Member
 
Join Date: Feb 2013
Location: East Flanders - Belgium
Posts: 8
Default Re: Paraset replica regen problem.

Thanks for the answer Alan.

I have bypassed the audio stage by listening directly onto the regen circuit with an earphone,and the 10kHz is still present. I noticed that the only thing I can do to affect the frequency of this signal is to add a variabel capacitor across the 1M grid resistance. adding a 100pF allows me to shift the frequency about 1KhZ while turning the shaft. (leaving the tuning capacitor in a fixed position of about 50pF).
HQsignals is offline  
Old 28th Mar 2015, 10:13 pm   #9
Guest
Guest
 
Posts: n/a
Default Re: Paraset replica regen problem.

Have a look at the HT decoupling.
 
Old 29th Mar 2015, 11:53 am   #10
Tyso_Bl
Hexode
 
Tyso_Bl's Avatar
 
Join Date: Jul 2014
Location: Magor, Monmouthshire, Wales, UK.
Posts: 436
Default Re: Paraset replica regen problem.

Can you show us what you're doing?
__________________
Adapt, Improvise, Oh Bother.....
Tyso_Bl is offline  
Old 12th Apr 2015, 12:25 pm   #11
HQsignals
Retired Dormant Member
 
Join Date: Feb 2013
Location: East Flanders - Belgium
Posts: 8
Default Re: Paraset replica regen problem.

Hi,

I'm currently seeking some time to have a look at the PSU decoupling/paraset. If possible I'll take a few pictures of the set I made and post it here.

regards,
Bjorn
HQsignals is offline  
Old 16th Apr 2015, 7:39 pm   #12
HQsignals
Retired Dormant Member
 
Join Date: Feb 2013
Location: East Flanders - Belgium
Posts: 8
Default Re: Paraset replica regen problem.

Hi all,

today I had a look at the B+ voltage of my paraset (about 360V when operating the receiver),with an oscilloscope.measuring a portion of the high voltage across a 1M resistor and potmeter of 22K,I was able to measure the B+ voltage on a 9V dc signal.

filtering out the DC with the oscilloscope,I was interested to see when happened on the AC side of the B+ signal.So this is what I could see so far:

1. potmeter regen all the way down (0V screen voltage)
-no AC present,a bit of hum of the PSU in the headphones.

2. increasing the potmeter untill the receiver starts giving the +/- 10kHz tone.
-as the regen potmeter increases,first there is no signal and then all of a sudden the B+ shows a clear +/-10kHz signal of at least a few 100mV Ptp.
It really jump out of nowhere, straight into the 10kHz oscillation at one point on the regen control.in the headphones I can hear the annoying 10kHz tone but almost no hiss or audio from the receiver.
-clear 10kHz sinewave on scope.

3. increasing the potmeter of the regen even further,untill audio is heard.
-further increasing the regen just a bit more gives more hissing and audio of received stations can be heard,while in the background the 10khz signal is clearly heard ,often louder then the received stations.
-the 10kHz sinewave is a bit distorted.It is now a sinewave with a small peak going positive first above Uptp,then it goes negative and follows the negative sinewave part.

4.moving the regen pot all the way up,gives more audio,but also more 10kHz signal in the headphones. received audio in the headphones is a bit distorted.
-10kHz sinewave gets more distorted,sinewave is a bit more flattened and the positive peak after the first part of the sinewave gets higher

*while increasing the regen potmeter,the frequency of the 10kHz signal keeps increasing as the the regen potmeter is increased.(up to max +/- 12kHz).


pictures to follow.

regards,
Bjorn
HQsignals is offline  
Old 29th May 2015, 10:48 am   #13
peter.sables
Rest in Peace
 
peter.sables's Avatar
 
Join Date: Dec 2007
Location: Doncaster, South Yorkshire, UK.
Posts: 385
Default Re: Paraset replica regen problem.

Hi.

Glad to see this posting. I've built 5 Parasets and with no problem at all. But this is giving me a pain. Its exactly as described. It can only be the valves now swapped every component. I'll tidy the set up then put new valves in.

I think one of the problems with this construction is that the drawing available are messed about. All saying original !. The parts are not numbered so a little discretion here . Some parts are marked uuf and others MMF. ! Also a electrolytic capacitor is marked as 2mf - .2mf even .2 none polarized. even voltage of 450v when at best its only 95v. The cap in series with the phones is either .01 or .05 mfd. Now just seen .10mfd is that .1mfds or ten.

A puzzle.

Pete G4MRU
peter.sables is offline  
Old 29th May 2015, 7:16 pm   #14
G3PIJpeter
Hexode
 
Join Date: Nov 2011
Location: Chippenham, Wiltshire, UK.
Posts: 319
Default Re: Paraset replica regen problem.

W7EKB says that he has identified at least five different versions of the Paraset schematic diagram floating about in cyberspace. His webpage at
http://www.w7ekb.com/glowbugs/tx/paraset.htm
includes a diagram (see thumbnail) of what he regards as an early Paraset. The TX includes a capacitive divider on the cathode (as Colpitts) plus a 'gimmick' feedback capacitor to the anode - guaranteed oscillation from any crystal!
- Peter
Attached Thumbnails
Click image for larger version

Name:	paraset.jpg
Views:	356
Size:	67.5 KB
ID:	108932  
G3PIJpeter is offline  
Old 29th May 2015, 10:28 pm   #15
peter.sables
Rest in Peace
 
peter.sables's Avatar
 
Join Date: Dec 2007
Location: Doncaster, South Yorkshire, UK.
Posts: 385
Default Re: Paraset replica regen problem.

Hi.

Yes it turns out to be the valve, in that it was the valve socket. After a clean it is now fine.

hi Pete G3PIJ. Yes I've seen this schematic. You could be right. It just backs up what I was saying. In the end if it works, use it.

pete G4MRU
peter.sables is offline  
Old 29th May 2015, 10:51 pm   #16
G3PIJpeter
Hexode
 
Join Date: Nov 2011
Location: Chippenham, Wiltshire, UK.
Posts: 319
Default Re: Paraset replica regen problem.

Quote:
Originally Posted by peter.sables View Post
Yes it turns out to be the valve, in that it was the valve socket.
I rely on a drawerful of old valve sockets for 'new' projects. It's worth giving each candidate a close inspection down the pin socket hole side with a 10X hand lens before installing - I have rejected many, especially octal types, where one of the two side 'fingers' has been mangled. Cleaned of solder, duff pins can be pushed out through the top of the socket on many designs for replacement by similarly liberated sound ones.
- Peter
G3PIJpeter is offline  
Old 1st Jun 2015, 11:23 pm   #17
peter.sables
Rest in Peace
 
peter.sables's Avatar
 
Join Date: Dec 2007
Location: Doncaster, South Yorkshire, UK.
Posts: 385
Default Re: Paraset replica regen problem.

Hi.

I've been looking into this Regen problem and found that .1mfds is the problem. It Must be an electrolytic and the value should be .2mfds (.22mfds)

pete
peter.sables is offline  
Old 6th Jun 2015, 4:06 pm   #18
peter.sables
Rest in Peace
 
peter.sables's Avatar
 
Join Date: Dec 2007
Location: Doncaster, South Yorkshire, UK.
Posts: 385
Default Re: Paraset replica regen problem.

Ha. foot in mouth... Still messing and now mine is working very well. That cap is now 25 mfds 50v. Still to make a contact though. Maybe 4 watts is too QRP.

Pete
peter.sables is offline  
Old 6th Jun 2015, 7:00 pm   #19
m0cemdave
Octode
 
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
Default Re: Paraset replica regen problem.

Quote:
Originally Posted by peter.sables View Post
Still to make a contact though. Maybe 4 watts is too QRP.
4 watts should be fine with a good aerial. I have just spent much of today with some of our radio club members operating a Paraset replica on 40m. We measured 2W output (it's only using a 250V power supply) and made solid contacts around the UK and France. Aerial was a 66ft dipole at about 15 ft. Some of the stations we worked were also running QRP (5W or less).

If you can get hold of some original 10X, 10XJ, or FT243 crystals, they will work better than modern ones. The new miniature types heat up and cause a lot of chirp. Also when tuning up, it helps to monitor your signal and tweak the anode variable for minimum chirp using a string of dots. Having said that, some chirp is an expected (and accepted) characteristic of a Paraset Tx.
m0cemdave is offline  
Old 7th Jun 2015, 11:05 pm   #20
peter.sables
Rest in Peace
 
peter.sables's Avatar
 
Join Date: Dec 2007
Location: Doncaster, South Yorkshire, UK.
Posts: 385
Default Re: Paraset replica regen problem.

Hi.

I think mine is as good as it will get. I did work DJ5RE last week so its not bad really and I got the QSL card also its nice to play. I think its not really a problem with the power as 4 to 5 wtts is not even one "S" point. I think the main problem is the re-gen. In the day time it sounds nice and even SSB comes in ok (no use though) But in the evening the CW is just mad. Yes I know about the crystals and to help get over that problem I put a 6v 40ma bulb in series. That works a treat.

Pete G4MRU
peter.sables is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:06 am.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.