Reproduced with kind Permission from Marcus
Another that turned out to be, “The yearly set from Hell”.
After some searching, I found out that the Howard chassis presented to me to attempt to fix was in fact manufactured by “Regent Radio Pty Ltd. According to the 1937 “Trade Annual” they were in Burke Road Camberwell. They were manufacturers of all types of radio receivers, public address amplifiers and transmitters. While that was all wonderful. It made no real contribution to sorting it out.
With the initial assessment, fortunately it looked like it had only two cathode electrolytics replaced and the originals, left under the tag board (tatty) and one resistor. Otherwise, a broken dial string and the dial glass itself cracked. The Pentagrid was missing along with the terminal of the fly lead for the 6G8 and a critical valve shield. All of the sockets were Octal: During the war there was a tendency to revert to the previous generations of old stock six pin types which I would suggest stopped “WD” scarpering off with them. Initially those sockets did help date it. Until I found the real info: But no circuit.
Amusing was, that when rolled on its back to inspect the underside, the inertia wheel of the tuning fell off. Its die cast like most and will eventually disintegrate. I did paint & glue it to slow the process. It was interesting to note that the Pentagrid was recessed in the chassis and it became clear that the set used to have an antenna post? That antenna area was a bit of a shemozzle.
It actually came with two speakers. The cone of the original electrodynamic was destroyed and a permanent magnet one was connected to the voice coil of the transformer. That made use of the field coil of the original electro-dynamic (Field coil) speaker. I was later to realise that the output transformer had an open primary and the valve tester did not like the 6V6 output tube, nor the 5Y3 rectifier. The 6G8 (second detector / first audio) fared little better. That meant a few new valves were in order. First IF was the forever cantankerous, 6U7. Leave one of them unshielded, at your peril.
One bad habit, poorly executed, was to place a link in the speaker plug to cut off B+ to the output valve Plate; should the speaker be left out. On some models without field coil speakers, that left the screen of any valve with one (Tetrodes, Beam Pentodes (Renodes archaic)), with a live screen. That meant that the screen became the plate, as it was not designed to handle plate current and it failed. In covering that likelihood; by cutting off all B+, the first cap is a 600v one, to resist the surge voltage, which will happen on startup anyway.
Irrespective of no circuit, I proceeded anyway. As normal the grid resistors of the 6V6 were way out of spec. They have an attrition rate, rather than a fail rate. Its cathode resistor also found the bin. So, three resistors went to the bin there. I was surprised as they all were types with a metal cap on their ends: I expected more failures. Being 50K, as expected the one on the Pentagrid and another resistor on the screens went. V1, assumed 6A8G; V2, 6U7G; V3, 6G8; V4, 6V6: V5,5Y3G
For some reason the original filter caps were still in circuit? Bad policy that can wreck the rectifier & probably did. They should have been replaced when the cathode bypass ones (2) were?
I ended up dismantling the field coil speaker and salvaging the coil. This was then mounted on the chassis and mods made to the speaker plug & socket to allow for that. The new output transformer was able to be mounted on the Permanent Magnet” speaker that came with it.
The dial globes were a 6V 5Watt automotive type. While these are gettable the damage to the dial glass did suggest that they were too hot. As both were blown and the grommets, they were in had started to break up, I decided to change these to a lower wattage conventional type at closer to 2watts. But saved the old sockets, in case that did not work out. The glass was removed, mainly to get the grot out.
Knobs were missing; however, I do have some from a closed factory that only needed drilling & tapping for lock screws. They will do until something better, or original turn up, or are made: Maybe?
Otherwise, getting it going was more an exercise in time. The paper caps were all leaking like a sieve as expected and were replaced; Along with all electrolytics. 6G8 cathode bypass cap was wrong, as it did not comply with the value of the old one still under the board.
Those I fished out, as there were paper ones under it, which needed replacing,it also looked less rushed & tatty. The 6V6 needed attention as it, and its grid resistors &cathode resistor were defective, as was the output transformer. This actually has a switched tone control. But otherwise, is relatively conventional for that run of valves, which wiring wise, tend to electrically follow the same, or similar plot. It was not powered as that was not considered safe, nor practical.
It did fire up with the usual corrosive issues with the pentagrid I used (6A8). This I guessed, by the fact it was Broadcast only and the pentagrids with their integrated triode exciter, did not appear till around 1938, mainly in muti-band sets thereafter: It was likely the rather unstable, 6A8: Any way it works. The RCA description of 2A7, 6A7 & 6A8 is not particularly flattering. The difference in those valves is the heaters and bases only. But it failed the “burn test”.
The NOS 6U7 was faulty with an unsoldered pin, on replacing with another tested one, I realised the socket was also broken, so out I came. Next came the realisation the First IF transformer had a make and break fault. That was a broken 100pF cap so I changed both. Now for the Pentagrid.
This particular valve 6A8 formerly several others mentioned in “RCA Handbook 1944”, is quoted as having good sensitivity on the broadcast band and on the SW bands down to 25 metres its sensitivity drops, rapidly falling off below 20 metres. It does not like AGC / AVC on short wave as it causes frequency shift. Which is largely why it was superseded by valves like 6J8, with separate triode oscillators built in, on SW. Voltage was another problem, as their oscillation is not very stable with variations in voltage.
Its socket also turned out to be faulty. Naturally the socket pins on the new, did not line up with the old socket, requiring some rewiring. Then one moved to the antenna & oscillator coils,
Initially I had noted that the Monkey had been at the front end. As noted, the aerial terminal had gone & was replaced by wire in a great tangle under the chassis. The oscillator was weak & playing up the 50Kgrid resistor inside the oscillators can had developed a loose cap and tested 100k, so out it went. I was hoping the fault was not a coil wire. Fortunately, it was a dry joint causing a “make & break”. The solder joint to chassis should have never been attempted, where it was: I moved it to a more effective point. Not surprisingly, the oscillator was much happier after that sort out. Modulation was much better.
That area needed a tidy up as the oscillator trimmer was a sky joint & it should have been bolted down? The holes were already in the side plate for both trimmers; so, I put it near the antenna one where it should have been. The trimmer was a bolt down type anyway? So why was it where it was? You could not turn the set on its side to adjust it, as that risked wiping out the 5Y3(see tube data)? It also impeded the tuning slug’s adjustment.
I did run it sideways while working on it, but used a Russian 5Y3, as its ruggedised & built more like a “6x..” rectifier series and has to have a cathode sleeve, by the way it behaves.
As it was a transformer set with a shielded transformer, which puts a charge on the chassis, it got a new cable which earthed / grounded its chassis. Much safer all round, & it did pass “Tag & Test” (Earth effective & no earth leakage).
Set is rather typical of the evolution from “Autodyne’s (Screen Grid Radios)” One of the first really successful super heterodyne radios, to ones using “Pentagrid” frequency changers, where mixing and oscillation were more predictable and superior. Unusual for the era, the highest BC frequency was 1600KHz which locally became 3NE around 1954. It’s now 1566KHz. IF I believe was 460KHz. I ended up tuning by the voltage method.
So, it did finally get to the point where it did not malfunction when “burn tested’ for a minimum of three hours. I did not have the cabinet. It was considered, by Sony, that three hours had the highest probability of failures.
Another that turned out to be, “The yearly set from Hell”.
After some searching, I found out that the Howard chassis presented to me to attempt to fix was in fact manufactured by “Regent Radio Pty Ltd. According to the 1937 “Trade Annual” they were in Burke Road Camberwell. They were manufacturers of all types of radio receivers, public address amplifiers and transmitters. While that was all wonderful. It made no real contribution to sorting it out.
With the initial assessment, fortunately it looked like it had only two cathode electrolytics replaced and the originals, left under the tag board (tatty) and one resistor. Otherwise, a broken dial string and the dial glass itself cracked. The Pentagrid was missing along with the terminal of the fly lead for the 6G8 and a critical valve shield. All of the sockets were Octal: During the war there was a tendency to revert to the previous generations of old stock six pin types which I would suggest stopped “WD” scarpering off with them. Initially those sockets did help date it. Until I found the real info: But no circuit.
Amusing was, that when rolled on its back to inspect the underside, the inertia wheel of the tuning fell off. Its die cast like most and will eventually disintegrate. I did paint & glue it to slow the process. It was interesting to note that the Pentagrid was recessed in the chassis and it became clear that the set used to have an antenna post? That antenna area was a bit of a shemozzle.
It actually came with two speakers. The cone of the original electrodynamic was destroyed and a permanent magnet one was connected to the voice coil of the transformer. That made use of the field coil of the original electro-dynamic (Field coil) speaker. I was later to realise that the output transformer had an open primary and the valve tester did not like the 6V6 output tube, nor the 5Y3 rectifier. The 6G8 (second detector / first audio) fared little better. That meant a few new valves were in order. First IF was the forever cantankerous, 6U7. Leave one of them unshielded, at your peril.
One bad habit, poorly executed, was to place a link in the speaker plug to cut off B+ to the output valve Plate; should the speaker be left out. On some models without field coil speakers, that left the screen of any valve with one (Tetrodes, Beam Pentodes (Renodes archaic)), with a live screen. That meant that the screen became the plate, as it was not designed to handle plate current and it failed. In covering that likelihood; by cutting off all B+, the first cap is a 600v one, to resist the surge voltage, which will happen on startup anyway.
Irrespective of no circuit, I proceeded anyway. As normal the grid resistors of the 6V6 were way out of spec. They have an attrition rate, rather than a fail rate. Its cathode resistor also found the bin. So, three resistors went to the bin there. I was surprised as they all were types with a metal cap on their ends: I expected more failures. Being 50K, as expected the one on the Pentagrid and another resistor on the screens went. V1, assumed 6A8G; V2, 6U7G; V3, 6G8; V4, 6V6: V5,5Y3G
For some reason the original filter caps were still in circuit? Bad policy that can wreck the rectifier & probably did. They should have been replaced when the cathode bypass ones (2) were?
I ended up dismantling the field coil speaker and salvaging the coil. This was then mounted on the chassis and mods made to the speaker plug & socket to allow for that. The new output transformer was able to be mounted on the Permanent Magnet” speaker that came with it.
The dial globes were a 6V 5Watt automotive type. While these are gettable the damage to the dial glass did suggest that they were too hot. As both were blown and the grommets, they were in had started to break up, I decided to change these to a lower wattage conventional type at closer to 2watts. But saved the old sockets, in case that did not work out. The glass was removed, mainly to get the grot out.
Knobs were missing; however, I do have some from a closed factory that only needed drilling & tapping for lock screws. They will do until something better, or original turn up, or are made: Maybe?
Otherwise, getting it going was more an exercise in time. The paper caps were all leaking like a sieve as expected and were replaced; Along with all electrolytics. 6G8 cathode bypass cap was wrong, as it did not comply with the value of the old one still under the board.
Those I fished out, as there were paper ones under it, which needed replacing,it also looked less rushed & tatty. The 6V6 needed attention as it, and its grid resistors &cathode resistor were defective, as was the output transformer. This actually has a switched tone control. But otherwise, is relatively conventional for that run of valves, which wiring wise, tend to electrically follow the same, or similar plot. It was not powered as that was not considered safe, nor practical.
It did fire up with the usual corrosive issues with the pentagrid I used (6A8). This I guessed, by the fact it was Broadcast only and the pentagrids with their integrated triode exciter, did not appear till around 1938, mainly in muti-band sets thereafter: It was likely the rather unstable, 6A8: Any way it works. The RCA description of 2A7, 6A7 & 6A8 is not particularly flattering. The difference in those valves is the heaters and bases only. But it failed the “burn test”.
The NOS 6U7 was faulty with an unsoldered pin, on replacing with another tested one, I realised the socket was also broken, so out I came. Next came the realisation the First IF transformer had a make and break fault. That was a broken 100pF cap so I changed both. Now for the Pentagrid.
This particular valve 6A8 formerly several others mentioned in “RCA Handbook 1944”, is quoted as having good sensitivity on the broadcast band and on the SW bands down to 25 metres its sensitivity drops, rapidly falling off below 20 metres. It does not like AGC / AVC on short wave as it causes frequency shift. Which is largely why it was superseded by valves like 6J8, with separate triode oscillators built in, on SW. Voltage was another problem, as their oscillation is not very stable with variations in voltage.
Its socket also turned out to be faulty. Naturally the socket pins on the new, did not line up with the old socket, requiring some rewiring. Then one moved to the antenna & oscillator coils,
Initially I had noted that the Monkey had been at the front end. As noted, the aerial terminal had gone & was replaced by wire in a great tangle under the chassis. The oscillator was weak & playing up the 50Kgrid resistor inside the oscillators can had developed a loose cap and tested 100k, so out it went. I was hoping the fault was not a coil wire. Fortunately, it was a dry joint causing a “make & break”. The solder joint to chassis should have never been attempted, where it was: I moved it to a more effective point. Not surprisingly, the oscillator was much happier after that sort out. Modulation was much better.
That area needed a tidy up as the oscillator trimmer was a sky joint & it should have been bolted down? The holes were already in the side plate for both trimmers; so, I put it near the antenna one where it should have been. The trimmer was a bolt down type anyway? So why was it where it was? You could not turn the set on its side to adjust it, as that risked wiping out the 5Y3(see tube data)? It also impeded the tuning slug’s adjustment.
I did run it sideways while working on it, but used a Russian 5Y3, as its ruggedised & built more like a “6x..” rectifier series and has to have a cathode sleeve, by the way it behaves.
As it was a transformer set with a shielded transformer, which puts a charge on the chassis, it got a new cable which earthed / grounded its chassis. Much safer all round, & it did pass “Tag & Test” (Earth effective & no earth leakage).
Set is rather typical of the evolution from “Autodyne’s (Screen Grid Radios)” One of the first really successful super heterodyne radios, to ones using “Pentagrid” frequency changers, where mixing and oscillation were more predictable and superior. Unusual for the era, the highest BC frequency was 1600KHz which locally became 3NE around 1954. It’s now 1566KHz. IF I believe was 460KHz. I ended up tuning by the voltage method.
So, it did finally get to the point where it did not malfunction when “burn tested’ for a minimum of three hours. I did not have the cabinet. It was considered, by Sony, that three hours had the highest probability of failures.
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