1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio - UK Vintage Radio Repair and Restoration Discussion Forum

howard · 22nd Jan 2012, 5:08 pm

Hello again,

I won this Dynatron Rally from Ebay recently for not a lot. I didn't power it up as the sheathing on the output transistor wires had melted and as I don't have a power supply with a current limiter the set was first powered up in Ron Bryan's workshop where it was found to be dead. Ron then did all the repairs to the chassis in this set so in his words, here's his account of the considerable amount of work needed to get this set working again. Trader Sheet 1798 covers this model and is available here for £1.99 ...

http://www.service-data.com/section.php/1899/1

Fault symptom:- Dead set, excessive current drain.

I powered up the set from 18V bench psu with o/p current limited to 20mA to avoid smoke and started to investigate.

The underchassis Newmarket output pair NKT271A / NKT772 were found to be shorted, with melted lead-out wire sleeving. The VA1040 thermistor and 4.7 ohm emitter resistors had been cooked, but tested ok. I temporarily replaced the o/p transistors with an AC127/AC128 pair, which fixed the psu short, but the bias current would not reduce to specified 4mA. The output was also distorted, although the mid point voltage was about right. Two resistors (R14, 2k2 and R18, 15k) were >20% high and were changed and the (two legged!) bias adjustment variable resistor was found to have gone up to 5k - it was replaced temporarily with a 500 ohm Bourns multi-turn trimpot which gave smooth adjustment, but did not fix the distortion. Finally the distortion was fixed by replacing the aforementioned AC127 which must have been faulty when I fitted it and the quiescent current was set to 4mA.

When setting the o/p stage quiescent current, I noticed that it increased by a couple of mA if the 'bass' button was depressed. Normally, the 12.5uf bass coupling electrolytic C17 is in series with C26, a 5000pF polyester cap, but for max bass this is shorted out. The electrolytic C17 had been fitted the wrong way round, causing unwanted leakage current to flow into the following DC coupled stages. This may be a production fault, as the Trader sheet shows incorrect orientation on the circuit diagram ie. the -ve end should go to the base of Tr5. There is no silk screening on the pcb to indicate the positive end. Anyway, C17 was tested for leakage, found ok and replaced with the correct orientation, which cured the problem.

The set sounded good after this except that the volume would not reduce to zero. A replacement unswitched 5k log pot was ordered from Bowood Electronics (arrived next day). The spindle was trimmed to length and the pot fitted. Luckily the TP37 has knobs with grub screws, so there was no need to file a new flat in the pot shaft.

Howard obtained a correct size, but three legged, 470 ohm Piher bias pot from Maplins and produced an AC187/AC188 pair from stock. These parts were fitted to the set, replacing the temporary components I had used for testing. One of the output transistors had to have a 0.030" brass shim wrapped around it to make it tight in the heat sink. The bias pot was fitted to the two mounting holes by bending the centre leg horizontal and linking that to one of the other pot legs on the pcb component side, then soldering the remaining two legs into the correct place.

A check on the set's performance showed that the tuning capacitor was shorting near full mesh and it was a little weak on LW. I adjusted the vanes of the tuning capacitor and was lucky enough to fix the short. It needed a slight movement to the aerial coil position on LW to peak up reception, but unfortunately the HF end of MW (around 1566kHz) just seemed to pack up, as if the oscillator had stopped. That meant that the OSC/IF LP1156 module had to be removed. It had been 'got at' before, so I was unsure what to expect. When I got the module out and removed the lid, I found that one AF117 had been replaced with an OC44! This must have just have been running out of steam at the HF end of MW in a design intended for alloy diffused transistors. I swapped all three transistors for AF126's, although in fact the other two AF117s were ok, and replaced the module. I made a small adjustment to the MW RF alignment and the set performed well on both bands.

I then returned the set to Howard for further work on the cabinet.

The case was in quite good condition but after 45 years it had collected a few dinks. These were all steamed out successfully and then the teak surfaces were cleaned with turpentine, sealed with linseed oil and finally treated with teak oil rubbed in using very fine wire wool. The dial and knobs were cleaned with upholstery cleaner and the dial then polished with Brasso and furniture polish. The chrome trim on the dial edge and the chrome metal parts of the handle were polished up with Brasso.

This is a good quality radio, especially its teak case which is excellent. It works very well too with good sensitivity and sound quality and its bass tone control button when pressed sure does give it some grunt !

Howard

bobbyball · 22nd Jan 2012, 5:45 pm

Another nice job!

Robert

Sideband · 22nd Jan 2012, 9:18 pm

Very nice! Well done for rescuing it and an excellent write-up. It seems to have construction similarities to Roberts especially with the Mullard module fitted. There may not be many of these about.

Rich.

Andrewausfa · 22nd Jan 2012, 10:06 pm

Nice work

I have one of these in green cloth and they do sound good.

Andrew

mark pirate · 23rd Jan 2012, 11:32 pm

That has come up a treat Howard, I have never come across one of these sets before.
I particularly like the wood cabinet.

Mark

howard · 23rd Jan 2012, 11:32 pm

Quote:

Originally Posted by Andrewausfa

Nice work

I have one of these in green cloth and they do sound good. Andrew

I've got one as well, a later TP42 I think it is with four rectangular push buttons. That too has Mullard module problems and its rear plastic grille has melted but the TP37 in the teak case is IMHO much the nicer version. Dynatron Rally sets are not that common but do work well once sorted so are definitely worth a look.

Howard

Hybrid tellies · 24th Jan 2012, 1:08 pm

I don't recall seeing this model before. Another brilliant job Howard and Ron.

newlite4 · 25th Jan 2012, 5:26 pm

Lovely, you can tell its a Dynatron because its such a fantastic looking set, nice one Howard.
Neil

22nd Jan 2012, 5:08 pm	#1
howard Nonode Join Date: May 2005 Location: Godalming, Surrey, UK. Posts: 2,593	1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio Hello again, I won this Dynatron Rally from Ebay recently for not a lot. I didn't power it up as the sheathing on the output transistor wires had melted and as I don't have a power supply with a current limiter the set was first powered up in Ron Bryan's workshop where it was found to be dead. Ron then did all the repairs to the chassis in this set so in his words, here's his account of the considerable amount of work needed to get this set working again. Trader Sheet 1798 covers this model and is available here for £1.99 ... http://www.service-data.com/section.php/1899/1 Fault symptom:- Dead set, excessive current drain. I powered up the set from 18V bench psu with o/p current limited to 20mA to avoid smoke and started to investigate. The underchassis Newmarket output pair NKT271A / NKT772 were found to be shorted, with melted lead-out wire sleeving. The VA1040 thermistor and 4.7 ohm emitter resistors had been cooked, but tested ok. I temporarily replaced the o/p transistors with an AC127/AC128 pair, which fixed the psu short, but the bias current would not reduce to specified 4mA. The output was also distorted, although the mid point voltage was about right. Two resistors (R14, 2k2 and R18, 15k) were >20% high and were changed and the (two legged!) bias adjustment variable resistor was found to have gone up to 5k - it was replaced temporarily with a 500 ohm Bourns multi-turn trimpot which gave smooth adjustment, but did not fix the distortion. Finally the distortion was fixed by replacing the aforementioned AC127 which must have been faulty when I fitted it and the quiescent current was set to 4mA. When setting the o/p stage quiescent current, I noticed that it increased by a couple of mA if the 'bass' button was depressed. Normally, the 12.5uf bass coupling electrolytic C17 is in series with C26, a 5000pF polyester cap, but for max bass this is shorted out. The electrolytic C17 had been fitted the wrong way round, causing unwanted leakage current to flow into the following DC coupled stages. This may be a production fault, as the Trader sheet shows incorrect orientation on the circuit diagram ie. the -ve end should go to the base of Tr5. There is no silk screening on the pcb to indicate the positive end. Anyway, C17 was tested for leakage, found ok and replaced with the correct orientation, which cured the problem. The set sounded good after this except that the volume would not reduce to zero. A replacement unswitched 5k log pot was ordered from Bowood Electronics (arrived next day). The spindle was trimmed to length and the pot fitted. Luckily the TP37 has knobs with grub screws, so there was no need to file a new flat in the pot shaft. Howard obtained a correct size, but three legged, 470 ohm Piher bias pot from Maplins and produced an AC187/AC188 pair from stock. These parts were fitted to the set, replacing the temporary components I had used for testing. One of the output transistors had to have a 0.030" brass shim wrapped around it to make it tight in the heat sink. The bias pot was fitted to the two mounting holes by bending the centre leg horizontal and linking that to one of the other pot legs on the pcb component side, then soldering the remaining two legs into the correct place. A check on the set's performance showed that the tuning capacitor was shorting near full mesh and it was a little weak on LW. I adjusted the vanes of the tuning capacitor and was lucky enough to fix the short. It needed a slight movement to the aerial coil position on LW to peak up reception, but unfortunately the HF end of MW (around 1566kHz) just seemed to pack up, as if the oscillator had stopped. That meant that the OSC/IF LP1156 module had to be removed. It had been 'got at' before, so I was unsure what to expect. When I got the module out and removed the lid, I found that one AF117 had been replaced with an OC44! This must have just have been running out of steam at the HF end of MW in a design intended for alloy diffused transistors. I swapped all three transistors for AF126's, although in fact the other two AF117s were ok, and replaced the module. I made a small adjustment to the MW RF alignment and the set performed well on both bands. I then returned the set to Howard for further work on the cabinet. The case was in quite good condition but after 45 years it had collected a few dinks. These were all steamed out successfully and then the teak surfaces were cleaned with turpentine, sealed with linseed oil and finally treated with teak oil rubbed in using very fine wire wool. The dial and knobs were cleaned with upholstery cleaner and the dial then polished with Brasso and furniture polish. The chrome trim on the dial edge and the chrome metal parts of the handle were polished up with Brasso. This is a good quality radio, especially its teak case which is excellent. It works very well too with good sensitivity and sound quality and its bass tone control button when pressed sure does give it some grunt ! Howard Attached Thumbnails Last edited by howard; 22nd Jan 2012 at 5:24 pm.

22nd Jan 2012, 5:45 pm	#2
bobbyball Octode Join Date: Jul 2011 Location: Stockport, Greater Manchester Posts: 1,215	Re: 1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio Another nice job! Robert

22nd Jan 2012, 9:18 pm	#3
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,578	Re: 1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio Very nice! Well done for rescuing it and an excellent write-up. It seems to have construction similarities to Roberts especially with the Mullard module fitted. There may not be many of these about. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

22nd Jan 2012, 10:06 pm	#4
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	Re: 1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio Nice work I have one of these in green cloth and they do sound good. Andrew __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member

23rd Jan 2012, 11:32 pm	#5
mark pirate Dekatron Join Date: Mar 2008 Location: Worthing, West Sussex, UK Posts: 5,185	Re: 1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio That has come up a treat Howard, I have never come across one of these sets before. I particularly like the wood cabinet. Mark

24th Jan 2012, 1:08 pm	#7
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,967	Re: 1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio I don't recall seeing this model before. Another brilliant job Howard and Ron. __________________ Simon BVWS member

25th Jan 2012, 5:26 pm	#8
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	Re: 1966 Dynatron TP37 Rally MW/LW 8 transistor battery portable radio Lovely, you can tell its a Dynatron because its such a fantastic looking set, nice one Howard. Neil __________________ preserving the recent past, for the distant future.