Kolster Brandes RV 10 (Crown)
 

Hi All,

I have treated myself to the world of 405 line TV by picking up a Kolster Brandes RV 10 (Crown) at a car boot sale :) Being 45 years old I apparently last watched a 405 line TV on a rented Rediffusion set in the early 1970s. I'm also new to this forum so go easy on me :). An image of my find is attached here.

Initial checks show a complete set. The EHT cage shows signs of being opened in the past and the CRT looks to be the original C17SM. One valve (PCC89) has gone gassy and a host of melty looking 'waxies' greet me. The tube appears to be stuck to the bezel on one side when attempting to pull the chassis.

I ask if I could be directed to a service sheet/schematic to purchase for this telly please - and if anyone can tell me their experiences of repairing these sets. They are generally good from what I have seen so far on the interweb.

Re: Kolster Brandes RV 10 (Crown)
 

The RV10 was a popular rental set, it was in fact made for that purpose. I remember the set well, very reliable and easy to service. Before you fire the set up I'd replace all those waxies in the frame timebase. Clip out the mains filter capacitor, it can be replaced later. Also replace the boost capacitor C63 (0.1mfd 500V) and C65 the A1 supply capacitor.(0.05mfd 1000V). These capacitors are easy to find, they are on a tag strips near the aerial socket.
I serviced a KB QF80 way back in 2011, this 21" set is similar in many respects to the RV10. I might be possible to search the forum for the restoration of this set.
Information for the RV10 can be found in the 1960/61 Radio and Television servicing book.

DFWB.

Re: Kolster Brandes RV 10 (Crown)
 

And here it is: https://www.vintage-radio.net/forum/...hlight=KB+QF80
The KB QF80 Majestic. The RV10 has a fireball tuner.

DFWB.

Re: Kolster Brandes RV 10 (Crown)
 

Thanks FERNSEH. Did you retain the selenium rectifier in your set?

Re: Kolster Brandes RV 10 (Crown)
 

The QF80. The original FC31 selenium rectifier had been replaced by a silicon diode of the BY127 type. The replacement diode along with an additional series resistor were fitted on to a piece of tag strip. The resistor can be 21 to 25 ohms 7watt. A 0.001 mfd capacitor was connected across the diode to protect it from mains borne spikes.
The FC31 is a contact cooled rectifier. Best replaced. The RV10 uses an RM5 finned rectifier, it could well be OK. If the smoothed HT is 228 volts and the unsmoothed HT is 235V I'd leave the old style rectifier in place. Boost voltage measured at C63 is according to the R & T book is 590 volts.

DFWB.

Re: Kolster Brandes RV 10 (Crown)
 

Thanks again :) I have just ordered a copy of J.P Hawker's 1960/61 Radio and Television servicing manual. I will provide regular updates on my progress. Tomorrow (hopefully) I intend to work on the cabinet, starting with a dose of woodworm killer and provide some 'before' pictures of the chassis.

Re: Kolster Brandes RV 10 (Crown)
 

I sorted a RV10 in 2005 and an RV30 which is very similar a while later.
https://www.vintage-radio.net/forum/...ad.php?t=61588.
https://www.vintage-radio.net/forum/...ead.php?t=6316
Both are still working very well. Hope you sort it out. Regards, John.

Re: Kolster Brandes RV 10 (Crown)
 

Here's an update on progress. I managed to pull the chassis/tube from the cabinet, (see pics). the gasket around the tube surround is still soft and in good condition. The chassis components look OK with no major heat damage or other mishaps. I now realise the valve that has gone to air with a crack in the base is a PCC89 in the socket for V4 (6BW7). A replacement 6BW7 will be ordered. I will check all the other valves shortly for the correct types. I have dismantled the cabinet, removing the front glass, bezel and liberally treated the woodworm infestation in the front baffle. The woodgrain effect appears to be a painted/printed effect in a dark brown. There are some deep scoring that's removed the grain effect. I was going to paint in the 'grain'. The varnish appears to be a cellulose lacquer - is this correct? Work on cleaning and recapping the chassis will start once the cabinet is sorted.

Re: Kolster Brandes RV 10 (Crown)
 

I think you have picked a good set for your first TV restoration, access to the bottom of the chassis is good and should be fairly straightforward to replace the capacitors and out of spec resistors.

KB build quality is high, and this set uses the excellent 'Fireball' tuner.
If the CRT is good, it should produce a cracking picture once restored.
:beer:
Mark

Re: Kolster Brandes RV 10 (Crown)
 

The more common EF80 can be used as a temporary substitute for the 6BW7 until the correct valve can be found. But it must be remembered that the IF alignment will be impaired when using the EF80. The interelectrode capacities differ.

DFWB.

Re: Kolster Brandes RV 10 (Crown)
 

Thanks Mark :) .

Re: Kolster Brandes RV 10 (Crown)
 

After a 3 year gap I am resuming action on this TV. As I don't have a 0.5mfd 200v capacitor (C60 in JP Hawker, p451) to hand. Can I get away with lashing 5 0.1mfd X2 caps in parallel instead?

Re: Kolster Brandes RV 10 (Crown)
 

I should have mentioned that the lashup I proposed in my post is just to get the set working as i still don't know if the tube is a runner. if the tube is good I will replace the lashup with a proper replacement. I have lots of these X2 caps to hand.

Re: Kolster Brandes RV 10 (Crown)
 

Well, unless anyone knows to the contrary, I'd say yes. The value should be the same, barring any weird stray effects. X2 is just a self healing ordinary capacitor.

Re: Kolster Brandes RV 10 (Crown)
 

I've done similar in the past as a test lash up, should be fine for a quick test. 3 year pause in a restoration and I thought I was the only one to do that! Now that reminds me must get on with recapping the IF section of that bush TV42 I started about 7 years ago.

Jay

Re: Kolster Brandes RV 10 (Crown)
 

Or you could just use a 0.47uF capacitor, as these are far more common.

Re: Kolster Brandes RV 10 (Crown)
 

sexton_mallard,

Have you given any thought as to how you will get a picture one that set once you have repaired it?

The Aurora standards converter is excellent, and works out of the box, but it is also many times the cost of your TV, and you have to make all your material available as a 625 line signal.

However, a Windows PC with the right graphics card is able to generate a 405 line output directly, and this is what I am doing here
https://www.youtube.com/watch?v=Q9b7_x0g0uM

All you need is a dual-head ATI Radeon HD 2400 Pro, and a VHF modulator, I built this
http://www.earlytelevision.org/405_modulator.html

Have a look at the posts by Peter Scott and myself in the "System converters" area of the forum, so far we seem to be the only two using this route.

Graham.
G3ZVT

Re: Kolster Brandes RV 10 (Crown)
 

It's hard to believe but I overhauled an RV10 back in 2005.

https://www.vintage-radio.net/forum/...ead.php?t=6316

That was twelve years ago, probably longer than it was used by it's original owner from new!

It still works very well on it's original tube. Took this picture a few moments ago. This particular section of my 'museum' has become somewhat cramped.
Oh dear..

Regards, John.

Re: Kolster Brandes RV 10 (Crown)
 

Thanks for the encouragement guys. I have now installed my novelty 0.5mfd cap, the next task is to replace the mains electrolytic with 100 and 470 mfd caps which is bulged and appears to have burst a small hole. I think this failure or the valve gone to air consigned the set to retirement and hopefully prevented many more hours on the tube. I have a working Sony 9-90UB (dual standard) running in 405 mode and produced some crude patterns and sound with a AF signal generator. At least this will give me some insight on the health of the set.

Hi Graham, your PC video + VHF modulator system is the route I may take. i wonder if a raspberry Pi could emulate something in place of the PC...

Re: Kolster Brandes RV 10 (Crown)
 

Nice thought, and I have three Pis here performing various tasks, but sadly the only people who really know what the Pi GPU can do will have signed a non disclosure agreement with Broadcom.
I know it don't sit well with the Open Source paradigm, but there it is.

Graham.
G3ZVT

Re: Kolster Brandes RV 10 (Crown)
 

i fitted the mains electrolytics with some jiggery-pokery and exending the wiring to allow me to solder all the connections without removing the tube from the chassis.

I powered up with a 42w lamp limiter ,then with a 150w bulb and saw signs of life, a rustle from the speaker from tuning the volume knob and tuner. Lots of nice glowing valve heaters and no smoke apart from a slight wisp from the dropper. Left the set running with a nice line whistle. Then switched to full mains via a isolation transformer. No light from the tube and the U26 EHT rectifier valve is cold with no signs of a lit heater. I checked the U26 which seems to have heater continuity and the valve base looks OK. So it could be the LOPTX heater winding?

Re: Kolster Brandes RV 10 (Crown)
 

The EHT rectifier (U26) heater winding is just a couple of turns round the line output transformer core in most cases. It has a very low DC resistance. So with the set unplugged and the CRT discharged, measure the resistance between the heater pin contacts in the U26 holder (valve removed). If it's open then there's a problem with the heater winding.

I don't know about this set (vintage TV is not my 'thing') but it's not unheard-of for there to be a low-ish value resistor in series with the rectifier heater winding. It's often hidden in the the rectifer socket housing. It can go open-circuit.

Re: Kolster Brandes RV 10 (Crown)
 

Check for RF at the EHT rectifier with a screwdriver.

Lawrence.

Re: Kolster Brandes RV 10 (Crown)
 

The heater winding seems to be fine with a low impedence, and again I checked the heater continuity on the U26. I traced the heater wires into the socket to be sure. There is no HT spark at all. I'm now thinking there is a problem on the primary side? I rechecked my recapping work and can't see any mistakes made.

Re: Kolster Brandes RV 10 (Crown)
 

Don't know about these sets off hand but certainly the later KB sets used a resistor in the EHT rectifier base which frequently changes value.

I remember the 21" Fernseh restored. Really was a lovely set.

Brian

Re: Kolster Brandes RV 10 (Crown)
 

After I posted my comment yesterday, I looked the set up in R&TVS. There is no EHT rectifier heater resistor shown there. However Sexton Mallard says that the winding is continuous at the rectifier base pins and that he can draw no HF arc from the U26 anode (or at least that's what I think he's saying).

Do you know that the overwind is continuous? Although if it were open, I'd still expect to get some glow from the U26 filament. I assume the line output valve isn't showing any signs of distress (red hot anode or screen grid, for example).

Re: Kolster Brandes RV 10 (Crown)
 

One old chestnut was the LOP valve screen feed, everyone carried a tin of 2.2K resistors.

Re: Kolster Brandes RV 10 (Crown)
 

The LOP valve PL81 does look to be working hard. In darkness a slight blue glow can be seen in side the electrode structure. The anode plates do look to almost be red but it difficult to see from the heater glow. I have never looked at one of these close up in a working set before so I don't really know what normal operation looks like. I appreciate the circuit has a lot of energy. Certainly the line whistle suggests this. I will take a picture later.

I could not get any arc from the anode cap of the U26, or from the connector either.

Re: Kolster Brandes RV 10 (Crown)
 

Can you draw a spark from the PL81 top cap using an insulated screwdriver?
If EHT is being produced then you should be able to do this.

Cheers

Re: Kolster Brandes RV 10 (Crown)
 

Hi Dom,
Have you managed to obtain a copy of the circuit yet? My R&TV servicing books are up in Essex so I do not have the circuit to hand but I assume it will be fairly conventional.
In order for the U26 heater to light, the whole line output stage needs to be working correctly. If it isn't, there is not sufficient energy to power the heater so it's a good indication that all is not well :(

The anode of the PL81 gets its volts via the primary winding of the LOPT from the cathode of the efficiency diode (PY81 or similar) The anode of this diode is connected to HT via a small inductor.

There is also a 'boost capacitor', one side of which is connected to HT, the other side goes to another connection on the LOPT. The boosted supply is often used to feed the frame oscillator, focus volts etc.
The boost is a useful place to measure what is going on in the output stage.
If I had the set in front of me I would proceed as follows:

1) Identify the boost cap from the circuit and ascertain which side of it goes to the HT supply and which side is the 'boosted' side.
2) Connect a meter to the 'boosted' side (1000V range) and switch the set on.
3) As the diode (PY81 etc) warms up you should get a reading of 200V or whatever the HT supply is.
4) As the PL81 starts to conduct and you hear line whistle, the reading on the meter should climb to about 650 to 750V. At this point, the U26 heater should light.

If you get no reading or a very low one on the meter, check that there is HT on the anode of the diode (PY81 etc). If there is, then the PY81 is probably faulty.
With the set running, check for volts on the screen of the PL81. As has been mentioned, the screen resistor (2k2 ono) can fail.
The PL81 itself could be faulty and as has also been mentioned, change the boost cap and also the coupling cap to the grid of the PL81.

If all this fails, then my suspicions would fall on the LOPT itself, but there are still a few more checks that can be done.

If someone would like to post the relevant part of the circuit, I could be much more specific as to where to measure and exactly what voltages would be expected!

Hope this helps and remember to be careful when measuring these high voltages.
All the best
Nick

Re: Kolster Brandes RV 10 (Crown)
 

Radio and TV Servicing. 1960/61.

Not a lot to wrong here. Check for man made faults when you carried out the capacitor change. Check screen grid, pin 8 of PL81 for voltage and scope the line drive waveform to pin 2. Run with the U26 [R20] disconnected to eliminate an internal short in the valve damping the LOPT. Does the LOPT get warm after 15 mins? I had a number of underwinds [primary] Fail on these models. John.

Re: Kolster Brandes RV 10 (Crown)
 

Thanks John, At least I can see what's going on!
The boost cap is the one next to the inductor in V8's anode (PY83). The boost supply from this is used to feed the frame oscillator via the height control and also the focus supply.
Other likely culprits are the coupling cap to the line coils and the two tuning caps in parallel across the primary.
Change the boost cap and the coupling cap in the grid of the PL81
Is the voltage on the triode section (line osc) of the PCF80 correct?
As John said, what is the screen voltage on the PL81?
Try changing the PCF80, PL81 and PY83.
Check that you get a low resistance between the top cap of the PY83 & PL81 through the primary of the LOPT (with the set switched off!!)
By the way, don't try and measure the voltage on either top cap- there are very high peak voltages and your meter will not like it 8-o
Let us know what happens after doing all that.
Good luck
Cheers Nick

Re: Kolster Brandes RV 10 (Crown)
 

Thanks for all the guidance gents! Here are some observations so far.

1. No arc can be drawn from the top cap of the PL81.

2. Resistance checks from the top cap of the PL81 and PY83 to chassis is about 2M Ohms, cap to cap about 10 Ohms.

3. Voltage from boosted side of boost cap is 235v. Removing the U26 makes no difference.

4. Pin 8 PL81 is at about 180v and the screen resistor R68 (4.7k in the book) mine measures 7K.

I left the set on for 10 mins to see if the LOPT was getting warm but the PL81 was definitely 'red plating' so I switched off! The LOPT remained cool despite being grilled from the PL81..

I shall carry on prodding when time permits. Watch this space.

Re: Kolster Brandes RV 10 (Crown)
 

Hi Dom,
If the boosted side of the cap is 235V that's just the HT being passed through the PY83 diode. So the PY83 is likely to be OK. If the PL81 is glowing, it's conducting heavily and as the screen voltage is reasonable, that current is flowing through the anode via the primary of the transformer. As you can't draw a spark from the top cap of the PL81, it would seem like the LOPT is being heavily damped. Sadly, this is most likely to be due to shorted turns either in the primary or eht overwind. Sorry about that :'(
It's still possible that the boost or other caps are faulty- I would change all the ones I mentioned in the above post if you haven't already done so. Also try replacing the 4k7 screen resistor, although with 180V, I doubt if it will make much difference.

Is it possible to disconnect the EHT overwind where it joins the tag for the top cap of the PL81? If the overwind is faulty, this can remove much of the damping and allow a spark to be drawn from the top cap of the PL81.

Try changing the caps first though and also measure the anode volts of the PCF80 line osc. Do you have a 'scope? If so (as John has already said) it would be useful to measure the drive waveform on the PL81 grid.
I really hope it's not the transformer but I have to say, its not looking too good!
All the best
Nick

Re: Kolster Brandes RV 10 (Crown)
 

All the current flowing through the PL81 will be flowing through the primary (between the two top caps). As this is only 10 ohms, the power will be quite small and probably won't generate much heat in 10 mins.
If the coupling cap from the anode of the line oscillator to the grid of the PL81 is leaky, the PL81 will certainly get hot and bothered- certainly worth changing.
Cheers
Nick

Re: Kolster Brandes RV 10 (Crown)
 

Clutching at straws, you earlier said that you have a line whistle. Do you also have -50 volts or so on the grid of the PL81?

Re: Kolster Brandes RV 10 (Crown)
 

Removing the actual connections from the overwind will have no effect if it has a s/c turn. To confirm this put a single loop of wire through the core of a working transformer and short circuit it while the receiver is working.
You will have to actually remove the overwind [not possible with the RV10 without destroying it] to make this test.
As Bill has mentioned, check the line drive waveform with a scope if you have one or check for a negative voltage [not quite so conclusive] at pin 2 of the PL81.

If you have any old LOPT from a scrap set, disconnect the line output and boost diode top caps and substitute the same connections on the spare transformer. Leave everything else in place. If EHT is now available at the spare transformers anode connection to the EHT rectifier, it is a good bet that the original has S/C turns.

This is probably why the RV10 was set aside a long while back. It's my guess that a Jellypot or other Thorn transformer would work OK but of course you have to experiment and understand what is happening in the circuits of the RV10 and the donor transformer. Recheck the boost capacitor connections just to be sure. John.

Re: Kolster Brandes RV 10 (Crown)
 

I get about -45 volts on the grid/pin 2 of the PL81. I do have a 'scope, i have never used one on a TV before but I am keen to learn :) I will dig it out to try later on. This might also seem a daft question but as I don't have a standards converter yet, I have been running the set with no actual signal. I seem to recall that TV timebases need a proper signal present even to trigger the 25 or so fps (frames per sec) screen refresh. Is this relevant to this model of set?

Re: Kolster Brandes RV 10 (Crown)
 

No. You should be able to get a complete raster without any signal applied to the input socket. Changing channels should produce clicks, pops and flashes on the screen. If you have a signal generator you can get something more interesting by feeding 45mc/s into the aerial socket, modulated that is and obtain bands on the screen and a sound signal at 41.5mc/s, channel 1 of course.

Don't worry too much about that at the moment. The line drive sounds good so I suggest you try a substitute hook up with another LOPT and let us know the results. John.

Re: Kolster Brandes RV 10 (Crown)
 

This evening I thought I might clarify a simple substitute LOPT test utilizing practically any line output transformer of any make.

The example I have here is from a Ferguson 506T I scrapped years ago. Before you start mourning it was filthy, disgusting, knobless and the cabinet was bashed to bits!

As you can see all I have done is remove the top cap connections from the PL81 and PY81 in this case a PYE V14C and connecting them via some croc clip extension leads to the corresponding connections on the Thorn 506T transformer. No other connections or disconnections were made.

As you can see good EHT is developed in the test transformer to the extent that the EY86 EHT rectifier lights up producing healthy EHT. This can be seen as I draw an arc from the anode connection. [Try holding a smartphone and drawing an arc at the same time]

I played around a bit more. If you don't have a scrap LOPT, delve down your junk box and find an old audio output or mains heater transformer. Connect the primary to the PL81 and PY81 [or any other timebase valves that may be incorporated in the test receiver] and the secondary to a 6.3v .3amp scale light lamp. As you can see with the line output stage working correctly the lamp will light.

This test will work with any receiver that has an independent line oscillator not dependent on any feedback pulse from the primary of the lopt.

It's a crude test but practical and will determine if the damped line output stage is due to shorted turns in the line output transformer itself.

With a little practice you can get to 'read' the results and arrive at a satisfactory conclusion. John.

Re: Kolster Brandes RV 10 (Crown)
 

What a great test using the heater Tx John, I like that a lot and will now perform this exactly as you have shown when I am in doubt about a LOPT!

:thumbsup:


Cheers

Re: Kolster Brandes RV 10 (Crown)
 

I lashed together John's tester with a spare RS audio output TX and I get a lit dial bulb ;D

The PL81 looks happy and does not seem to be overheating if I leave this rig running for a few minutes. Turning the horizontal hold which changes the line frequency also dims the bulb slightly with higher the frequency.

I'm going to triple check all my work around this end of the set - as you may have seen from other threads I have slipped on a few banana skins before!

Re: Kolster Brandes RV 10 (Crown)
 

I think I've misunderstood the purpose of the test. Is the lashup is in effect simulating the heater overwind and as the PL81 seems OK this indicates the fault is indeed in the LOPT but the of the stage is running OK?

Re: Kolster Brandes RV 10 (Crown)
 

The test with the substitute transformer will prove that the line output stage is driving the output valve as it would with the correct transformer.
Obviously if the scan coils are S/C or there is anything loading the PRIMARY of the RV10 transformer this test cannot detect that as these components are out of circuit!

Knowing the KB chassis I would say by your remarks that the LOPT is faulty.

It's worth disconnecting all leads from the LOPT primary tags and run the test. This will definitely confirm a faulty LOPT if it is heavily damped with the PL81 anode glowing a dull red.

Hope this helps. J.

PS Did you get those crocodile clips from RS components? I like them!

Re: Kolster Brandes RV 10 (Crown)
 

Glad you like my croc clips. Almost fully biodegradable and heat resistant.

I reconnected the top cap leads with the 'tester' still connected and witnessed the following. The bulb comes up to full brightness for about 1/3 of a second then suddenly dims when the line whistle comes up, the filament then goes down to a dull glow. on switch off the bulb then blinks briefly for about 1/3 of a second before going out. If there is a S/C I would not expect the bulb to light to beyond a dull glow or not glow at all.

Re: Kolster Brandes RV 10 (Crown)
 

I disconnected the white and orange leads to the LOPT primary. The EHT rectifier heater came up which seem to confirms the primary is faulty. I don't want to give up on this set. I'm now thinking of the feasibilty of a rewind or a transplant.

Re: Kolster Brandes RV 10 (Crown)
 

OK. This is odd. The test lamp cannot light unless the transformer is being driven at line rate via the PL81.

If you have disconnected the primary and you now have EHT it appears to me that either the scan coils are shorted, [very unlikely but possible] or you have a fault in the wiring.

Check C60 .5uf scan coupling capacitor, the two 40pf 5kv capacitors, C62/C64 for S/C. The later two may be of a slightly differing value. These are 3rd harmonic tuning caps the values of which were adjusted to stabilize transformer 'spread'.

Other than that it may well be the transformer but if the primary has a shorted turn, even when disconnected the circuit would be heavily damped and would not produce EHT. John.

Re: Kolster Brandes RV 10 (Crown)
 

Hi,
this thread is very useful, as it gives me a lot of background info I wouldn't be able to get anywhere else. As I have a couple of Older sets to look at when I get " a round tuit "

Re: Kolster Brandes RV 10 (Crown)
 

Thanks John. I ran the set in darkness and could see a blue discharge from the end of the white disconnected wire to the primary and could hear a faint hight voltage 'tearing' noise from the speaker. The PL81 looks rather impressive with a slight blue glow. I switched off and got a bright but not intensely bright spot from the screen which is encouraging as the tube could be OK :).

I did look for any arcs or sparks from the scan coils which are very loud! What sort of resistances should I get for each?

The disc caps don't test S/C and nor does the .5 cap which I lashed together with 5 0.1 X caps. I shall carry on checks tomorrow.

Re: Kolster Brandes RV 10 (Crown)
 

Mmmm! OK run the chassis with just the scan coil connections disconnected at the coils themselves leaving all connections to the transformer in place. You should be able to get some EHT and a vertical line on the screen.

Remember that the frame timebase will probably be in poor condition due to leaky capacitors but once again you should be able to see some frame deflection if you adjust the height and frame hold controls.

The focused blue glow in the PL81 is quite normal as it is with almost all line output valves. If the timebase runs OK with the coils disconnected it points to shorting turns but I would not take a bet on it.

I'm not sure what you mean when you say' the scan coils are loud' together with the arcing from the white wire. Was the arc to free air or to a connecting tag? J.