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13th Jul 2010, 4:03 pm | #21 |
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Re: GEC BT1156 First Light & Vidor CN4216
Had a little poke around the GEC today, I hooked up the new KVM and the A2 reads at 7KV (also confirmed with another KVM borrowed from Malc to verify mine) this should be typically around 12KV for the 7204A GEC CRT.
The A1 was at 298V which is good, typically it should be 300V so that's pretty much spot on. The MR1 was at 187V and the multi smoothing can started at 180v & 170V settling at 187V & 175V. Is it likely to be the U25 I have a new one obtained from Malc today but I did'nt just want to whip the old one out until I've exhausted all possible tests but I'm not sure what they might be. Teleman has provided me with some resistors to check but that's around the line osc and hold issues that I have. I don't have a circuit for this set the nearest is in RT&S 1957/58 page 351 but no mention of the 1156 only a circuit for the 2253 Without this or a trader i'm not sure but I'm wondering if the HT is down 20+V which would account for the missing 5KV, there again I could be talking complete tosh. Chris Last edited by oldticktock; 13th Jul 2010 at 4:27 pm. |
13th Jul 2010, 6:51 pm | #22 |
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Re: GEC BT1156 First Light & Vidor CN4216
Measure the HT and find out then. That's the best way.
If the A1 is OK then the HT is probably OK. The EHT valve has probably passed it's best. Cheers, Steve P.
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13th Jul 2010, 6:56 pm | #23 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Steve,
I thought that's what I had done measuring the voltages on the Metal rectifier and the smoothing can. But without the trader I was unsure of what voltage I should have. I assumed 200V+ so my readings were below that. |
13th Jul 2010, 8:00 pm | #24 |
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Re: GEC BT1156 First Light & Vidor CN4216
Just a thought but if the HT should be about 200V and I'm getting about 185-187V measured on the metal rectifier, could it be MR1 is faulty?
Is this a selenium rectifier (see pic) I've heard much about. I have a IN4007 I could put in place, I know I would need to add a forward voltage drop resistor in series. I don't have a 100R 5W but I do have a 68R 10W or a 120R 7W. does this make sense and would the resistors be ok? or am I talking nonsense. I'm confused due to the A1 being almost spot on. Chris Last edited by oldticktock; 13th Jul 2010 at 8:28 pm. |
13th Jul 2010, 8:47 pm | #25 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris,
It could be getting dragged down due to a fault...try measuring what the current drain is. You could use that 68R & stick it in series with 4 of those 120R resistors in parallel - that'll give you nearly 100R. I'm waiting to see that Vidor powered up - I've been up in the loft today & I resisted the temptation to dig mine out...infact, I've been putting a few things back up there as there is starting to get too much clutter around the house. |
13th Jul 2010, 9:01 pm | #26 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Techman,
You know I always forget my lateral thinking, I have 200R 4W so 2x those in parallel, thanks for the boot up the rear to wake me up. I guess I should just give it a try, just don't like disturbing things especially if i'm barking up the wrong tree. I like to air my thought process first to see if i'm learning or not. I have a circuit for the GEC BT2253 and HT on that is stated at 205V P.s As for the in and out the loft issues you have do what I did and move in with them |
13th Jul 2010, 9:50 pm | #27 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris , I would'nt be tempted to change the HT rectifier just yet, as mentioned in an earlyer post there could be a fault pulling down the HT, have you changed the N308 / PL36 ? & check the screen feed resistors R117 3.9k & R116 100 ohm. looking at the circuit the boost line should be 520volt at lopt pin 1. I have had c130 350pf give trouble in my set its a high voltage silver mica . all the best ,Chris..
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13th Jul 2010, 10:09 pm | #28 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris,
Ok won't make the change. No N308 in this set, I have a Line ouput valve which is a 30P19 ,an efficiency diode which is a Mazda U191. I was at Malc Scotts today dropping off a valve and getting a U25 and mentioned the weird valves in this set, and the lack of details in trader and RT&S R116 ok R117 ok Will check boost and find the C130. Edit: Powered on, 50 seconds later line whistle heard Boost measures 270V, 2 mins later Aurora test tone heard Boost measures 332V, about 1 min 20secs later raster appears Boost measures 344V, It's slowly climbing whilst I was type this, now it stands a 369V and climbing very slowly now Many thanks for your help. Chris Last edited by oldticktock; 13th Jul 2010 at 10:36 pm. |
13th Jul 2010, 10:55 pm | #29 |
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Re: GEC BT1156 First Light & Vidor CN4216
Chris the valve you quote for line output N308 matches the RT&S for the BT1155, BT2253 and BT3252. The EHT rectifier in the book is U47.
My set seems to have totally different valves. Is this by design or mistaken changes by former owners, this is where the schematic for BT1156 would help. I checked some valves, V10 the RT&S states it should be a Z329, it actually is Z329 V5 RT&S states should be Z329 actual is Z329 V6 & V4 RT&S states should be Z329 but are EF80's I'm guessing these are equivs but my valve data book does not list them as such. V9 RT&S states should be a Z329 but actual is a 6/30L2. EHT Rec RT&S states U47 actual is a U25 V15 RT&S states N308 actual Line output is 30P19 V18 RT&S states U339 actual efficiency is U191 Last edited by oldticktock; 13th Jul 2010 at 11:03 pm. |
13th Jul 2010, 11:36 pm | #30 |
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Re: GEC BT1156 First Light & Vidor CN4216
If I could get over to the reference section here, I'd see if I had a circuit for a GEC BT1156. I'll see if the wife is willing tomorrow.
But looking at the pictures you got at first switch on, I would look at the Line Oscillator stage as it appears to be running at the wrong speed. This could lower the EHT a bit as well. Cheers, Steve P.
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13th Jul 2010, 11:56 pm | #31 | |
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Re: GEC BT1156 First Light & Vidor CN4216
Quote:
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14th Jul 2010, 12:03 am | #32 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris,
strictly speaking a Z329 is equivalent to a 30F5, which is equivalent to a PF818. These all have the same base connections as an EF80 and are very similar to it but with slightly higher gm and a 7.5v 400mA heater. EF80 is a passable emergency swap. A 6/30L2 is a double triode so definitely nowhere near equivalent to any of the above, and therefore it's a very odd substitution unless there's been a significant modification either by the makers or a previous owner. Or somebody's fitted a valve into a socket to fill the gap just to make the set "complete". More investigation needed here methinks. Pete |
14th Jul 2010, 7:00 am | #33 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi, G8KBG Tony
sometimes I wonder about my sanity!!! Ok so looking at that someone has been playing silly with the valves. As far a I can tell the set has not been modified all components seem to be in spec except the valves! Looks like I need 6x Z329 2x N369 1x N308 1x U339 1x B319 1x B729 Last edited by oldticktock; 14th Jul 2010 at 7:13 am. |
14th Jul 2010, 8:38 am | #34 |
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Re: GEC BT1156 First Light & Vidor CN4216
Just noticed a slight whoopsie in my mail re 30F5/PF818... these of course have a 7.5v 300mA heater, not 400mA.
Sorry about that. Pete |
14th Jul 2010, 9:18 am | #35 |
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Re: GEC BT1156 First Light & Vidor CN4216
Cheers Pete,
I'm the whoopsie master, cannot beleive RT&S boo boo I think the person who sold me this just stuck in what they had to make it look complete, what amazes me is that I had a sort of testcard in post #1 although it quickly went. I do pick em! Don't think I will do anything else to this set until I have the correct valves in circuit. Hopefully Malc down the road can assist. chris Last edited by oldticktock; 14th Jul 2010 at 9:26 am. |
14th Jul 2010, 9:45 am | #36 | |
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Re: GEC BT1156 First Light & Vidor CN4216
That was me talking doo doo's again V9 is meant to be a B729
Quote:
My U191 (Eff diode) is an ok sub for the U339 so that's another. Chris Last edited by oldticktock; 14th Jul 2010 at 9:57 am. |
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14th Jul 2010, 12:31 pm | #37 |
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Re: GEC BT1156 First Light & Vidor CN4216
All the valves in the GEC BT1155 and BT1156 were manufactured by Mazda, perhaps with one exception, the DH77, which could have sourced from a number of valve manufactures.
GEC insisted on designating their valves with the older Marconi-Osram system. The B729 is really a Mazda 6/30L2. the ECC804 is a Pro-Electron designation used by Brimar. GEC N308 = Mazda 30P4 or 30P19.= Brimar PL302. Be carefull using the PL36, it has certain internal connections which are brought out to certain pins. GEC U339= Mazda U191. GEC Z329 RF pentode = Mazda 30F5. The 14" 90 degree 7205A CRT is an equivalent of the Mazda CME1402. GEC N369 = Mazda 30P12 beam tetrode. GEC Z77 = Mazda 6D2, also EB91 and 6AL5. Interesting to note that GEC produced an earlier 14" model, the BT1155. This set has a similar cabinet as the BT1156. The main difference is the CRT which is a 14" 70 degree type 7204A. This CRT is similar to the Mazda CRM144. The BT1155 has a hand wired chassis. DFWB. |
14th Jul 2010, 12:42 pm | #38 |
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Re: GEC BT1156 First Light & Vidor CN4216
Wow! thanks David, that's cleared up a great deal of confusion for me, so the only odd valves I have in circuit are the EF80's which should be 30F5's.
Also the Line Ouptut I have (30P19) is ok, my reduced Boost (down by 140V) is down to some other component then. Looking at the circuit my HT is down by 20V too. I will do some more checking and persue Telemans advice on the other bits. I would have preferred the BT1155 as I don't like this new fangled PCB that's come along, my first encounter with it and yuk! Once again thanks Chris P.S. how's the Korean coming along (best reply pm as well off topic) Last edited by oldticktock; 14th Jul 2010 at 12:51 pm. |
14th Jul 2010, 1:07 pm | #39 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris,
I wouldn't be too concerned about EF80's instead of 30F5's for now, they do work as a replacement. If you suspect they are affecting i.f. alignment when the set is working, or if there's a specific problem, then maybe look for some then. As the EHT and width slowly increase over some minutes of operation it's more likely to be a worn out valve (line output or boost diode) than one of these causing the fault. A metal rectifier is always suspect for low HT voltage, so well worth bridging in a silicon replacement... even if it's only temporarily whilst you prove the point. I think Ferseh means D77= 6D2= 6AL5 = EB91, so don't get confused again ! [Z77 = EF91] If you are certain the line o/p valve and boost diode are good, check the G2 feed resistor for the 30P19 and the anode load resistor in the line oscillator. Also, check the 30P19's grid 1 leak resistor to chassis, that it hasn't gone very high. Pete |
14th Jul 2010, 1:11 pm | #40 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Cris,
According to the circuit diagram of the BT1156. The boost voltage should be 520 volts at pin 1 of the line output transformer. The boost capacitor, C131 (0.05mfd) is connected to pin 1 of the LOPTx and the main HT line. The first anode voltage of the CRT is supplied from the LOPTx via a 2.2Meg resistor R131. Capacitor C135 (0.5Mfd) is the CRT A1 supply decoupler, like C131, one end of the C135 is connected to the HT line which should be 205 volts. Check components C131, C135 and R131. Confirm that the HT volts are between 195 to 220. Have you checked C110 (0.01Mfd)? It's the capacitor that couples to line oscillator to G1 of the line output valve. The line drive waveform to line output valve should be 100 volts P-P. The DC reading at G1 is -50 volts or slightly more. With regard to the 30F5/Z329 valves. The EF80 can be used certain circuit positions such as the line osc. sync separator and video amplifier. Try to use the correct valve in the IF stages. Remember that the 30F5 has a 7.3 volt heater. EF80 is Vh 6.3V. DFWB. |