Decca SG177 Stereogram - restoration, retrofitting tweeters?

[wpl955g]

Hi all,

I recently picked up a Decca SG177 Stereogram with the optional ESS/2 slave speaker and am starting to put it back to rights. 25 October 1958 is stamped inside the case, and I'd like to have her ready in time for her 60th birthday party.

As you can see, she's had a bit of a hard life; the once pale blue case is gummy and yellowed from years of cigarette smoke, the optional atomic legs are no more, and the plastic grille looks to have been melted by a carelessly placed candle, which may have hastened its retirement to some distant loft years ago...

However, she's cleaning up tolerably well with baking soda and warm water, and I have an idea about restoring the colour to the original leather cloth. As for the grille, the plan is to use the one on the slave speaker to create a silicone mould and fabricate a new one with polyurethane plastic. I may fabricate two to ensure the colour matches... and hey, the mould will make great Decca ice cubes later. I've also invested in some 15" legs and she's starting to look a bit more like herself.

It's fitted with a BSR Monarch UA12 with the TC8S stereo cartridge, which still works. After a good bit of cleaning, lubricating and adjustment the turntable runs beautifully and sounds pretty good through another amp. I've not had a look at (and have resisted the urge to plug in!) the amp - a four valve job (2x ECL82, an EZ81 and an ECC83) with 5w output (2.5w a side), according to the specs - but that's next on my list. Caps and resistors all around! Will keep you posted - and may need some advice...

As for Retrofitting, I'm wondering about the advisability of modifying the speakers by adding tweeters. I was reading a post here about someone who knew an old TV repairman who claimed to have fitted them to a Hacker model with a 2.2uF bipolar electrolytic cap to give it a bit more treble, and am having a think about a similar kind of modification here.

The main unit and slave speaker are both fitted with Alnico Celestion 4x6 inch full range D68JQs (3 ohm marked on each), and having tested them with another amp I can report they sound pretty sweet. (If anyone knows anything in particular about these, I'd be much obliged, but I don't expect they're anything special.) There's room enough inside both the main unit and slave to fit a tweeter (up to 4") and I've a chap on eBay selling some Celestion tweeters of the same vintage.

75% of me says to leave it original, but then there's that 25% that figures I'm going to be tearing her down and putting in the work to make her the best she can be, and maybe that should extend to a little upgrade for her next sixty years.

Anyway, thanks in advance, and any thoughts appreciated!

[Edward Huggins]

I think there's a typo, the main Celestion speakers are 8" x 6".
A 2.2 cap offers an ideal filter frequency and it may be still possible to buy 3" cone tweeters. If not, there are the "Lookalike-Audax" dome tweeters now being heavily discounted at Maplins. Those 3 stage single-ended amps should have sufficient sensitivity if you decide to replace the BSR TC8S crystal for a more compliant, "modern", ceramic type e.g. BSR SC11M.

[RojDW48]

I restored an SRG500 a while ago - a bit more sophisticated, console style but with the same deck and cartridge. I found (with advice from the forum) that the stereo performance of the TC8S was greatly improved by a drop of acetone on the 'cushion' that supports the stylus shank - it helps to revive the rubber. Nevertheless it might be worth thinking about a kinder cartridge, maybe the SC12S. The TC8 is great with 78s but there are better stereo options. The Celestion drivers in the SRG500 might well be same as yours and they sounded really good - bearing in mind I had the radio option and I set it up to accept a CD player as well. I didn't feel the need to add tweeters. What I am trying to say is - I don't think the TC8 will perform well enough to justify tweeters in the first place and the Celestions Decca chose are surprisingly good.

[dseymo1]

Perhaps the ?4" tweeter used in the Deccalian 88 might be a good match, if you can find a pair.

[wpl955g]

Thank you both, that's hugely helpful! Oddly enough, I'm more of a 78 man than anything, with some decent but not special 50s jazz 33s, but I may pick up a SC12S to save them the trouble. But the Deccalian 88 had a tweeter? They're not dissimilar mdels... wondering if Decca used the same case layout but fitted different components depending on the model, which would have made sense... May leave it for a while and mull it over, especially as I'm thinking I might rig in a parallel Bluetooth amp, or at least a line in, to give it a bit more versatility.

Cleaning progresses well, but you can see what I'm in for with getting the colour back. The grey has held up well, but between the nicotine and natural fading that blue has really gone on the top. On the plus side, I've managed to almost completely remove scorching from a big cigarette burn on the lid.

Originally Posted by Edward Huggins

I think there's a typo, the main Celestion speakers are 8" x 6".
A 2.2 cap offers an ideal filter frequency and it may be still possible to buy 3" cone tweeters. If not, there are the "Lookalike-Audax" dome tweeters now being heavily discounted at Maplins. Those 3 stage single-ended amps should have sufficient sensitivity if you decide to replace the BSR TC8S crystal for a more compliant, "modern", ceramic type e.g. BSR SC11M.

Yep, typo, apologies. 8x6, not 6x4. Thanks too for the Lookalike Audax tip, will keep my eyes out. Even if I don't install them, I might just try them out for sound and see what happens.

[Edward Huggins]

Glad to help. If there is no way of cleaning the top of the lid and you don't want to recover, I would not be too proud to carefully match a matt/semi matt white emulsion with a grey/blue blend sampler pot. Allow for the colour to alter when dry.

[RojDW48]

I can see from your latest pics that your cabs have the dished front. I think that was an exciting new innovation for the 60s! My favourite old Decca is a Deccalian from around 1946, which has essentially the same cab but with a straight front, so they kept that design going for a long time. Mine has the lovely 6V6G single ended amp and I converted it to play 33s etc with a muti-speed deck.

I also added a line in for CDs etc with a switched mini stereo jack socket (wired for mono in my case). That was quite straightforward to do.

I have an SG188, which has the same balance/output panel at the back. When 2 separate speakers are attached there it switches out the 2 mid range drivers in the cab but retains the bass driver. The satellite speakers are very pretty little things, again with Celestion drivers, and the central bass works really well. I wonder if yours has a similar arrangement?

[wpl955g]

I've barely had a look at the electrics, but it seems that all that happens when you plug in the satellite speaker is that it splits the signal from mono to stereo. The schematics explain that the Channel A & B plugs are there to accommodate your placing the speaker to the left or right of the main unit and selecting the right channel.

I'm curious. When you installed your input for the CD player, did you put in a voltage divider/resistors to take the edge off? I used to have a 1929 DeForest Crosley tallboy radio with a Phono input that needed a potentiometer in line to keep line level down (and it sounded superb!) but I'm not sure this amp won't be more forgiving. Guess I'll find out in due course!

[RojDW48]

Interestingly - no. The original 78rpm cartridge was a magnetic one with an output of around 30 mV with a step up TX in line to the volume control. To accommodate the ceramic cart in the new deck I bypassed the TX and that worked well, so the switched jack socket just dropped into the input line and it sounds very good indeed.

Yes, of course, your arrangement at the back is for selecting which way round you want the stereo image to work. The SG188 just looks the same. I had it working for quite a long time without satellite speakers before I thought - 'where's the balance control?' (it produces a surprisingly good stereo image from the 2 internal speakers - only about 12" apart). When I located it I gave it a tweak and nearly jumped out of my skin! I don't think it had ever been turned since made in 1958! Servisol cured the heartstopping row......so be warned!

[nigelr2000]

Have sent you a PM re:a new (to this player) speaker grill

[Edward Huggins]

Originally Posted by RojDW48

Yes, of course, your arrangement at the back is for selecting which way round you want the stereo image to work. The SG188 just looks the same. I had it working for quite a long time without satellite speakers before I thought - 'where's the balance control?' (it produces a surprisingly good stereo image from the 2 internal speakers - only about 12" apart). When I located it I gave it a tweak and nearly jumped out of my skin! I don't think it had ever been turned since made in 1958! Servisol cured the heartstopping row......so be warned!

When you say a stereo image from the 2 internal speakers, I don't quite understand this. Do you mean there are seperate LH and RH channel speakers inside the one cabinet - OR - the main speaker and tweeter from just one channel?