Classic Hifi Care

Hello Guys, This afternoon I fired up the CG and again the two bigger rectifier tubes on the left amp are loose and don't light up. If I wiggle them they light up and the left channel comes in. I did it with out power this time as I am scared of electrocution. However I am wondering if there is a common temp fix for this or is this new tube sockets time? Hydro

All four of the rectifier tube sockets in the amplifiers of my Concert Grand have been replaced some time during its lifetime, before I got it. Whoever did the work, did it quite neatly, used ceramic sockets with stainless steel, fine-threaded bolts to hold them to the chassis. My only theory as to why they were replaced would be that the 5U4 tubes are fairly heavy and are mounted horizontally. The weight of the tubes, combined with chassis heat, may impact the connections on the tube pins unfavorably. Wafer tube sockets may not be able to stand the stress. The good side of all this is there is plenty of room to work, and ceramic tube sockets are not terribly spendy. Using a Dremel tool to grind off the rivets, you should be able to do the job with a minimum of damage to the chassis. Good luck.

In addition, my CG has most of its original tubes in the amps, except the rectifiers. Those are Sylvanias.

Hydro, you should generally be safe from high voltage working on the topside of the chassis. The UNDERSIDE of the chassis is where the high voltage resides. I always recommend following your voltmeter when working with a chassis with unknown voltages, or where you suspect high voltage may be present. Better safe than sorry.

With the power switch off, and with the power plug of the Concert Grand removed from the wall outlet, remove the rectifier tubes. Then, using needle nose pliers, gently squeeze the tube socket terminals together to make them a bit tighter, giving them a better grip on the tube pins. This might be all that's needed to get you going again. If you continue to have trouble, then the tube sockets may have to be replaced.

Edit....I forgot to mention something. It might be a good idea to clean the tube sockets for the rectifiers while you are in there. The chassis plating on Magnavox chassis has been known to migrate into the tube sockets, causing poor connections. If you have access to cutting torch tip cleaning brushes they make excellent tube socket cleaning brushes. Good luck.

Yeah, I was going to add the "squeeze the socket terminals" advice. And the advice to unplug before working. There was the old advice about working around high voltages--always keep one hand in your pocket so you're not completing a circuit. It's like working on the table saw. I always try to stay a bit worried.

Chris Campbell

Hydro, did you make any progress on the tube issue in your CG? Inquiring minds want to know......

Hello, Have not done anything cause of covid. I did however look on the internet and saw these https://tubedepot.com/products/retainer ... 4-6ca7-6l6 What do you think of these ?

Those are not horribly expensive, so they might work fine. And we might all learn something that will help in the future.

electra225 wrote: ↑Sun Nov 06, 2022 1:27 am Those are not horribly expensive, so they might work fine. And we might all learn something that will help in the future.

I already did. They have an "octal tube keyway replacement" that fits over the pins on tube with a broken key post. I always figured I was the only one with broken keys on tubes.

Chris Campbell

If you should use the fine brushes to clean the sockets, I'd recommend using 91% isopropyl alcohol with them to clean them. It washes away tarnish on the silver plated sockets. It does the same on silver plated wafer switch contacts.

Hello all, The other day I got the idea to try another set of SU5GB tubes in the CG's left amp so I took 2 out of the continentals AMP 182 no problem now so far they have stayed in and working. Hydro

Does anyone make tube retailers for 12a..7s and other small 9 pin tubes?
My Zenith 3B70 amp's preamp has an upside-down 12AX7 that I worry about potentially falling out.