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Old 2nd Nov 2019, 12:32 pm   #81
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Default Re: VE301W Radio help

Thanks for hunting that out and testing it Rob, but I'll give it a miss.
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Old 2nd Nov 2019, 12:47 pm   #82
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Default Re: VE301W Radio help

It's directly heated, so can you see the filament clearly and does it look to be the correct brightness, Rob? If not then it could have a high resistance in one or all of the pin connections. If it's normal brightness it might still be worth remelting the solder in the anode pin and the other two just for good measure - you know what these old valves can be like in this respect. I usually file the very ends of the pins with a fine file until I can actually see the end of the inner wire shining to make sure of an absolute connection when re-soldering.
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Old 2nd Nov 2019, 1:13 pm   #83
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Default Re: VE301W Radio help

OK. The silver gettering covers all the glass, so nothing visible.
I just tried it on my bench psu and at 4v the current is correct at 1A. I tried reflowing pins, as expected, no luck. In my CT160 with 4.5v it rises to about 25 on the scale and with 5v about 35.
So, a no hoper really.
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Old 2nd Nov 2019, 1:21 pm   #84
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Default Re: VE301W Radio help

Yes, I know what you mean about the gettering on these old valves, that was the problem with the valve that I mentioned in a previous post in that it had a filament short to grid, but I couldn't actually see it through the glass. It's not just the getter silvering, it's also that dark deposit caused by the early process of coating the filament with a special cathode emitting substance - I forget the name of it now, think it began with a 'Z', someone will know. Shame about the valve, but at least you've now tried all the options.
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Old 2nd Nov 2019, 2:08 pm   #85
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Default Re: VE301W Radio help

Quote:
Originally Posted by robinshack View Post
Hi Graham, It is a Mullard DU10, but tests extremely low unfortunately. CT160, Vf 4v, Ia 60mA settings as book. See picture.
You can still have it if needed?
Rob
Sorry to muck you about Rob, but I see that the RGN 354 has a spec for 25mA of anode current and the AVO data book suggests testing at 15mA.

Would you mind testing the DU10 valve (60mA) again at 15mA.

Thanks, Graham.
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Old 4th Nov 2019, 10:15 pm   #86
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Default Re: VE301W Radio help

The capacitor box was lined with MDF to give it rigidity and support the lid.

New capacitors were soldered to the lid. These were all tested prior to fitting, including an electrical leakage test at the full working voltage. Having carefully checked their position and polarity I refitted the lid and reattached the can to the chassis by bending the fixing tabs back to their original positions.

The broken lead from the inter-valve transformer was soldered back on to its tag on the capacitor block. The lead was drum tight, probably why it broke in the first place, so I extended it.

A new three core mains lead was fitted. The plug was fitted with a 1A fuse, the set's internal fuse being rated at 0.5A.

The screen grid dropper resistor was replaced as its value had increased from 100k to 170k.

The speaker leads were renewed. I decided to fit the tone correction capacitor across the speaker terminals rather than under the chassis.

The contacts of the wave change switch were cleaned with fine glass paper followed by a squirt of Servisol 10. I don't like switches like these with non-wiping contacts. although it has to be said there's a lot of contact pressure when the contacts are closed.
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Old 4th Nov 2019, 10:34 pm   #87
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Default Re: VE301W Radio help

Time to apply some power, initially with no valves fitted.

On switch on there were no bangs, flashes, smoke or smells. It pays to do basic testing before applying power. I confirmed that LT and unrectified HT were present on the secondary windings of the mains transformer. I left the set like this for about ten minutes feeling the transformer's laminations from time to time. They remained completely cool to touch.

Next I fitted just the rectifier valve. This came from my own set as the rectifier valve which came with the set is u/s. I connected my DMM across the smoothing cap and switched on. HT voltage was present, but a bit high as no current was being drawn. As expected there was no voltage across the 700R bias resistor which is connected in series with HT negative.

I fitted the other two valves from my own set, as they were known to be good. The shack aerial was connected to one of the MW sockets. No earth connection was required, as this is now supplied by the mains lead.

A few seconds after switch on the set came to life with half a dozen stations received on MW and BBC Radio 4 on LW.

I still have a lot of work to do to complete the repairs, of which more later.
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Old 4th Nov 2019, 11:10 pm   #88
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Default Re: VE301W Radio help

Hi Graham,
Interesting to follow your progress with this restoration. Nice neat job with the capacitor box- I assume originally, the 2 & 4mfd caps would not have been polarised electrolytics? Actually, I'm not sure when electrolytics were developed but I guess they will work just fine in this circuit application!

I see your new 3 core mains lead. Are you giving any thought to the fact that the highest mains tapping is for 220V? I've been wondering what to do about that on my own set. What are your thoughts on the various options, which are to run it on 240V, fit a resistor in the primary or run it from an external 220V transformer? I was also considering fitting a thermal fuse in close contact with the primary winding as extra protection in case of shorted turns.

All the best
Nick
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Old 4th Nov 2019, 11:29 pm   #89
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Default Re: VE301W Radio help

I have been watching this thread with interest and found it educational to read about the stepped approach you took before finally applying power with valves installed. The advantage is clear especially as the transformer status was something of an unknown quantity, but it also means each stage of the power supply can be independently verified at each step. I have noted for future reference!

It would clearly have been impractical to have guided the OP through this repair on the forum and I look forward to your next installment.
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Old 7th Nov 2019, 2:15 pm   #90
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Default Re: VE301W Radio help

Quote:
Originally Posted by 1100 man View Post
Hi Graham,
Interesting to follow your progress with this restoration. Nice neat job with the capacitor box- I assume originally, the 2 & 4mfd caps would not have been polarised electrolytics? Actually, I'm not sure when electrolytics were developed but I guess they will work just fine in this circuit application!
I didn't conduct a detailed post mortem examination of the capacitor block's innards, so I can't say whether the capacitors were unpolarised or not. The fact that no polarity signs are shown on the circuit points to that being the case though.

It can be a bit tricky to get one's head round the PSU circuit of these radios. The HT line is drawn below the chassis line and I prefer to see this at the top. Also a 700R resistor is connected in series with the negative side of the HT supply to derive bias for the output valve. Once this is understood it's easy to see that this is a conventional CRC smoothing circuit and to work out which way round to connect the electrolytic capacitors.

Quote:
Originally Posted by 1100 man View Post
I see your new 3 core mains lead. Are you giving any thought to the fact that the highest mains tapping is for 220V? I've been wondering what to do about that on my own set. What are your thoughts on the various options, which are to run it on 240V, fit a resistor in the primary or run it from an external 220V transformer? I was also considering fitting a thermal fuse in close contact with the primary winding as extra protection in case of shorted turns.

All the best
Nick
I wonder if any of these sets have been damaged or has their life shortened as a result of being used directly on UK supplies? I use a Variac during testing/repair, but have also connected my own set directly to the UK mains supply. For JUSTDAMO's set I'll probably fit a dropper resistor in series with the primary winding of the mains transformer, making the mod easily reversible.
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Old 7th Nov 2019, 2:23 pm   #91
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Default Re: VE301W Radio help

Quote:
Originally Posted by WaveyDipole View Post
I have been watching this thread with interest and found it educational to read about the stepped approach you took before finally applying power with valves installed. The advantage is clear especially as the transformer status was something of an unknown quantity, but it also means each stage of the power supply can be independently verified at each step. I have noted for future reference!

It would clearly have been impractical to have guided the OP through this repair on the forum and I look forward to your next installment.
When it comes to repairing sets, especially someone else's, I'm a slow methodical plodder. I pride myself on my technical knowledge and like to use it.

Changing all caps and out of spec resistors would not have got either of the VE301W sets I've repaired working. My own set had an open circuit speaker coil. JUSTDAMO's set had a disconnected inter-valve transformer and a duff rectifier valve. Both easily diagnosed faults.

It surprises me that some members will happily change all the two wire components in a simple one or two valve record player amplifier, but are then completely stuck when it doesn't work afterwards. A few preliminary measurements with a DMM would have saved them a lot of trouble.
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Old 7th Nov 2019, 2:24 pm   #92
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Default Re: VE301W Radio help

You should use a bucking transformer to reduce the 240V mains to 220V. Any 20V transformer will do as it will only need to be rated for about 250mA.
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Old 7th Nov 2019, 2:39 pm   #93
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Default Re: VE301W Radio help

The OP has a limited budget. Added to which lack of space inside the radio means that a bucking transformer would have to be located externally which would mean an enclosure etc.
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Old 7th Nov 2019, 5:37 pm   #94
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Default Re: VE301W Radio help

Time to take a break from the electronics to sort out the cabinet, knobs etc.

I wedged open the crack in the case as much as I dared and forced Araldite Precision two part epoxy adhesive into the gap. The wedge was then withdrawn, the excess adhesive wiped off and masking tape used to hold the gap tightly closed. The cabinet was then placed in a safe place to allow the adhesive to cure.

Once the adhesive had set, the cabinet along with the knobs were cleaned and polished as described in this post:-

https://vintage-radio.net/forum/show...20&postcount=5

Now to tackle the warped tuning scale which I assume is made from celluloid. Experience has taught me that this material can be softened in boiling water, but this has a detrimental effect on the embossed lettering, or should I say numbering?

The scale was placed on a flat surface, in this case a piece of Melamine faced chip board, and heated evenly with hot air gun until it was too hot to touch. A this point a heavy steel "washer" was placed on it to hold it flat. It is important that as well as being flat the tuning scale is at 90 degrees to the shaft in all directions. A long dummy shaft was inserted into the scale's boss and held in the correct position until the scale had hardened again.

The result is not perfect, but run out is sufficiently small to prevent the scale disengaging from the pulley on the tuning knob.
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Old 8th Nov 2019, 3:32 pm   #95
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Default Re: VE301W Radio help

With the cabinet sorted it was time to get back to the electronics, starting with the RGN354 rectifier valve which had a full heater to anode short.

I decided to try blowing away the short. Wire was wrapped around the heater pins shorting them together. Then a car starter battery was connected between heater and anode. There was an orange flash within the envelope and I thought it most likely that the heater had burned out. Checks with a DMM on ohms range showed this was not the case. The heater had continuity and there was an open circuit between heater and anode.

I plugged the rectifier into the radio and it worked, but only for a couple of minutes whereupon the radio died. A quick test showed that the heater had shorted to the anode once again, so I repeated the car battery treatment. This time the valve worked for about four minutes before it stopped rectifying as evidenced by mains hum form the speaker. Time to give up on the valve and try another approach.

A 1N4007 diode in series with a resistor seemed the way to go. Calculating the value of the resistor isn't easy and it's best to use trial and error methods to determine its value. I fed the set from a Variac set to give 220 VAC. Then I measured the voltage at the reservoir capacitor which according to the service sheet should be 265VDC. A 680R resistor gave a reading of 260 VDC which was close enough. The resistor is rated at 2 watts so should safely handle 54mA which was about four times the current it's likely to see in practice.
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Old 8th Nov 2019, 4:01 pm   #96
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Default Re: VE301W Radio help

The envelope of the RES164 pentode output valve had become detached from the base. I plugged it into the set, but there were just clicks and crackles from the speaker. Gently wriggling the envelope found a sweet spot where the received signal was heard from the speaker. It was obvious that there was an intermittent short or open circuit within the base.

I unsoldered the base by sucking the solder out of the pins. When separating the parts of a valve like this it is important to note the orientation of the base with respect to the envelope and the positions of the wires leading to the electrodes. Only the heater wires can be identified electrically and it's very difficult tracing the wires through the pinch to the electrodes.

There was no sign of an open circuit and I noticed that two of the wires crossed each other with one being insulated with sleeving. I decided to sleeve all the wires before soldering the base back on again. The envelope was then temporarily secured to the base with masking tape.

When the valve was plugged into the set it worked just fine. The louder sound from the speaker suggests that it has more emission than my own output valve. As a more permanent repair the envelope was fixed to the base using adhesive lined, heat shrink sleeving.

Finally the OP's REN904 RF triode valve was plugged into the set and worked first time.
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Old 9th Nov 2019, 6:00 pm   #97
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Default Re: VE301W Radio help

Can I ask Graham,what is that you use adhesive wise to secure the valve envelope back to the base?

I know someone said not Superglue.

Thanks
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Old 9th Nov 2019, 6:17 pm   #98
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Default Re: VE301W Radio help

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As a more permanent repair the envelope was fixed to the base using adhesive lined, heat shrink sleeving.
I didn't use any "glue" to stick the envelope to the base. The hot melt glue on the inside of the heat shrink tubing sticks very firmly to the envelope and base, then shrinks to hold the two in intimate contact. The valve does not get very hot in use, so it's unlikely that the glue will soften.

I was concerned that heat or shrinkage might crack the glass, but this did not happen.

I understand that the military repaired valves using this method.

I have used two part epoxy (Araldite Precision) in the past, but the heat shrink does a better job IMHO.
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Old 9th Nov 2019, 6:24 pm   #99
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Default Re: VE301W Radio help

Thank you Graham.
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Old 10th Nov 2019, 8:43 pm   #100
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Default Re: VE301W Radio help

Almost there.

The remaining paper? capacitors, all with values in pF, were changed. This didn't improve the performance of the set, but should improve its reliability. They'd all gone high in value and two had cracked cases, just the thing to let moisture in. When tested at 500V two had no leakage at all and one had very slight leakage.

The tuning knob spindle had a displaced 'C' clip, if you can call a flimsy piece of metal a 'C' clip! I suspect it came out of the groove when a "tight on the shaft" tuning knob was removed. I fitted a proper circlip.

Experiments showed that a 390R resistor was needed to drop the mains voltage from 240VAC to 220VAC. I only had a two watt resistor and it was running a bit hot for my liking. I've ordered a 390R 15W panel (chassis) mounted resistor, which should be here on Tuesday.
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