Well the replacement CL33 valve arrived safely via Royal Mail (even though the package wasn't marked as fragile) and earlier today I had another go at powering up the SUG91 chassis.
The valve heaters glowed once again, and the HT came up to around 245V on the rectifier cathode. Everything began to look good, but the loudspeaker remained suspiciously silent. After a couple of quick checks with the AVO it became obvious that the primary of the output transformer was open circuit!
I thought that I had checked that earlier in the restoration... but perhaps not.
I'm a bit suspicious that both of the faults have been around the output stage. Perhaps the valve suffered a catastrophic failure (excess grid current caused by a leaky capacitor perhaps) and took out the transformer?
So now I'm looking for a replacement, and the radio will have to stay unfinished for a while longer.
Keep listening!
Friday, April 18, 2014
Sunday, April 13, 2014
Not quite as I hoped...
I had hoped to get the Bush SUG91 completed this weekend, but unfortunately I found a fault that had not been picked up during the restoration.
On powering it up for the first time (via an isolating transformer, because in this set mains neutral is connected to chassis) I was greeted by a nice bright pilot lamp, but no glowing valve heaters. All the valve heaters are wired in series, and as expected one was open circuit; unfortunately it was the CL33 output pentode, which I don't have in stock.
I managed to get one from the usual internet auction site, so hopefully in a few days I will be able to get it working.
I did manage to finish the cabinet though, and I'm very pleased with how it looks.
On powering it up for the first time (via an isolating transformer, because in this set mains neutral is connected to chassis) I was greeted by a nice bright pilot lamp, but no glowing valve heaters. All the valve heaters are wired in series, and as expected one was open circuit; unfortunately it was the CL33 output pentode, which I don't have in stock.
I managed to get one from the usual internet auction site, so hopefully in a few days I will be able to get it working.
I did manage to finish the cabinet though, and I'm very pleased with how it looks.
I've deliberately left a few blemishes and imperfections, as I wanted it to look used but cared for, rather than brand new. I was thinking of selling this one when it was finished, but now I like it so much that I might keep it.
Details of the electronic restoration will follow, so come back later if you want to know what it took to get this one working again.
Keep listening!
Friday, April 11, 2014
Fixing Woodworm Holes
I mentioned in an earlier post that my Bush SUG91 cabinet had suffered from woodworm sometime in its history.
During restoration of the cabinet I realised that if I filled the holes with wood filler, the filler would be a different colour than the surrounding wood after I had applied wood stain. I believe that some types of filler will take a stain, but not any of the ones that I had in my workshop.
My wife came up with a brilliant idea; dip a cocktail stick into PVA glue, she said, and poke the stick into the wormhole. Once the glue dries, cut off the stick close to the surface of the wood, and sand down whatever remains standing proud.
Brilliant idea! It worked really well, and after applying the stain the repairs are almost invisible.
Keep listening!
During restoration of the cabinet I realised that if I filled the holes with wood filler, the filler would be a different colour than the surrounding wood after I had applied wood stain. I believe that some types of filler will take a stain, but not any of the ones that I had in my workshop.
My wife came up with a brilliant idea; dip a cocktail stick into PVA glue, she said, and poke the stick into the wormhole. Once the glue dries, cut off the stick close to the surface of the wood, and sand down whatever remains standing proud.
Brilliant idea! It worked really well, and after applying the stain the repairs are almost invisible.
Bush SUG91 Cabinet Restoration
The old damaged veneer came off easily. After using a heat gun to gently soften the glue, I was able to peel the damaged veneer off with a craft knife blade. A quick sanding removed all traces of the old glue and left a smooth surface ready to accept the new veneer.
One large piece was fixed onto the top surface using PVA glue. I then clamped another piece of wood on top to keep the veneer flat whilst the glue dried. For the two curved surfaces I used contact adhesive, as clamping these in place while PVA dried would have been very difficult. The glue I used allowed a small amount of movement before bonding firmly, and I cut the veneer to shape as closely as I could before applying the glue.
I allowed the glue to dry overnight before carefully removing the excess veneer with a very sharp craft knife blade. The rough edges were then sanded down using fine sandpaper on a wooden block.
This was my first attempt at applying veneer, but on reflection it went better than I had expected. The finished result looked pretty good, although I didn't get a perfect clean edge between two joining pieces on the top surface. A lot of sanding was required to get a smooth surface ready for lacquering
The cabinet sides and bottom panel originally had a very dark brown lacquer finish. Unfortunately the new veneer is a different shade than the original, so to reduce the final number of colours I decided that a new colour scheme was needed. The front and control panel were just sanded and re-lacquered; all other surfaces were treated with dark oak stain before lacquering.
Once the lacquer has hardened I will give it a polish and then start re-assembling. I'll post more details and photos later.
Keep listening!
 |
| Damaged veneer removed |
One large piece was fixed onto the top surface using PVA glue. I then clamped another piece of wood on top to keep the veneer flat whilst the glue dried. For the two curved surfaces I used contact adhesive, as clamping these in place while PVA dried would have been very difficult. The glue I used allowed a small amount of movement before bonding firmly, and I cut the veneer to shape as closely as I could before applying the glue.
 |
| Top and one side complete |
I allowed the glue to dry overnight before carefully removing the excess veneer with a very sharp craft knife blade. The rough edges were then sanded down using fine sandpaper on a wooden block.
This was my first attempt at applying veneer, but on reflection it went better than I had expected. The finished result looked pretty good, although I didn't get a perfect clean edge between two joining pieces on the top surface. A lot of sanding was required to get a smooth surface ready for lacquering
. |
| After staining |
Once the lacquer has hardened I will give it a polish and then start re-assembling. I'll post more details and photos later.
Keep listening!
Tuesday, April 01, 2014
Another Bush radio
I picked up a Bush SUG91 radio for £10 in December, and its been sitting in my workshop ever since. I believe that this type of floor standing sets were known as 'console' sets. It's a big old beast, but with its 10" speaker and large cabinet I'm hoping it will sound good.
This is the first set in my collection that I have been able to date exactly; a quality control label inside shows that it passed its final test on 27th January 1947.
The chassis looks very similar to a Bush DAC90, but with the addition of shortwave and a gram input. The SUG91 is an AC only set, but with an auto-transformer instead of a proper double wound transformer. I'm not sure why this was, as the cost saving must have been very small. (There was also an AC/DC version called the DUG91 which used a dropper resistor)
As with AC/DC sets though, the mains neutral is connected to chassis, so it will need the usual safety precautions taking. There is plenty of space in the cabinet, so I might fit an isolating transformer inside if I can find something suitable.
I can't find the photo that I took before starting work, so this is one of a similar set from the internet. The cabinet was in pretty good condition, but there were a few woodworm holes in one side, and an area of damaged veneer on the top left front edge. I don't think there were any live woodworm left, but just to be safe I gave it a good soaking with woodworm killer, wrapped it in a plastic bin liner and left it in the garage for a few days before bringing it into the house.
The chassis came out a few weeks ago. since then it's been cleaned, re-capped and had some wiring replaced. Over the last few days I have stripped down the cabinet, removing the speaker baffle, control panel and the decorative trim round the tuning scale; these all came out easily after removing screws.
Removing the damaged veneer was easier than I expected, but getting the old lacquer or varnish off has been a bit of a problem. I think I'll leave that story for another day.
Keep listening!
This is the first set in my collection that I have been able to date exactly; a quality control label inside shows that it passed its final test on 27th January 1947.
The chassis looks very similar to a Bush DAC90, but with the addition of shortwave and a gram input. The SUG91 is an AC only set, but with an auto-transformer instead of a proper double wound transformer. I'm not sure why this was, as the cost saving must have been very small. (There was also an AC/DC version called the DUG91 which used a dropper resistor)
As with AC/DC sets though, the mains neutral is connected to chassis, so it will need the usual safety precautions taking. There is plenty of space in the cabinet, so I might fit an isolating transformer inside if I can find something suitable.
 |
| Bush SUG91 radio |
I can't find the photo that I took before starting work, so this is one of a similar set from the internet. The cabinet was in pretty good condition, but there were a few woodworm holes in one side, and an area of damaged veneer on the top left front edge. I don't think there were any live woodworm left, but just to be safe I gave it a good soaking with woodworm killer, wrapped it in a plastic bin liner and left it in the garage for a few days before bringing it into the house.
The chassis came out a few weeks ago. since then it's been cleaned, re-capped and had some wiring replaced. Over the last few days I have stripped down the cabinet, removing the speaker baffle, control panel and the decorative trim round the tuning scale; these all came out easily after removing screws.
Removing the damaged veneer was easier than I expected, but getting the old lacquer or varnish off has been a bit of a problem. I think I'll leave that story for another day.
Keep listening!
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