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Discussion in 'Amp Tech Center' started by Si G X, Feb 6, 2020.
I look forward to restoring it for you.
I look forward to following your progress. It's a sweet little amp and deserves to get restored.
I'm tempted to knock up a little T/V-6 head - I have a few EF86's (Mullard, Siemens, Winged C, at least) and EL84's (and a spare EZ80) laying around that could be fun to roll on that platform.
Jon, what's your opinion on valve vs. ss rectification on small SE amps? I mean, they can't really sag by their SE nature, so is there any noticeable difference? I like valve for authenticity, but ss saves a heater and some real estate for little/no pertainable effect on tone. Obviously I mean in an HT adjusted design - not spiking your B+ by 40VDC
I had a Twin Selector tone back around ‘64, it was the same grey as the OP’s one. Never appreciated it at the time, complete teenage ****.
The Selmer arrived this morning a few hours ago and this is the progress so far;
I will attach some photos but the meter I use has an Organic Display and my camera has trouble with flicker.
What we do is lift the 250R resistor on pin 3 of the EZ80 and place a 1M 1W resistor in series. With only the EZ80 fitted and as there is no bleed resistor we turn it on and wait for the voltage across the 1M to drop to less than 50volts. 1M with 80volts across it is 800uA leakage.
Then if all goes well we use a 100k 1W resistor and wait until the voltage reads less than 25v = 250uA leakage.
If it gets that low then the main smoothing has almost reformed and will probably not need replacing. Any more than 50volts and it will require more time to try and recover.
If 300volts was applied to an old electrolytic, it is likely to get hot spots inside, as there will be no current control and likely to be damaged.
If all does not go well with the capacitor can reforming, I usually remove the insides and replace it with three capacitors internally with lead outs at the top and then re pot it.
That keeps it original looking.
But so far so good!
The leakage has settled at 18volts across a 100k = 180uA very respectable.
I will leave it soaking now for a couple of hours and check again before the next stage,
replacing the other two electrolytics and checking the resistors before testing the EF86, EL84 and EZ80 on my Avo VC160 valve emissions tester.
Just tested the valves, the EL84 is toast, it has an internal short circuit. A new one is not the end of the world. EZ80 is good, Photo attached of my valve tester and the EF86 is good also.
A Svetlana USSR 16P14P-EV which is what I normally fit as they have a slightly larger power output than the standard EL84 or a Mullard EL84 New Old Stock but not cheap.
Probably best to see what needs replacing component wise first but I am always happy with the USSR valves.
Hi Jon, ah that's a shame... oh well.
A Russian is fine with me... I have all modern Russian valves in my Marshall (EHX and Tung-Sol) and they've been great.
I hope to use the amp, so I can't be too precious about the valves as I know they don't last forever.
Svetlana 6П14П-ЕВ (6P14P-Ev) is an excellent tube. Basically a Soviet Milspec (JAN) longlife valve from the best of the Soviet factories (Svetlana/Winged C quality is several cuts above the stuff Mike Matthews is producing now in the old Reflektor factory).
I would definitely go with that, and if you're curious about how Mullard/Brimar/Phillips etc. might change the tone then pick up a couple of lightly used specimens on eBay. Warning, once you start valve rolling you'll never stop
Jon - watch out for the EF86 being microphonic. They have a bad rap for that as I'm sure you know. But the Selmer schematic looks to run the EF86 more conservatively than Dick Denney ever did, so likely it's not so susceptible.
Not as bad as horrible JJs!
Was that in reference to microphonic EF86s or New Sensor/Reflektor valves or did I miss something ? Do you dislike/mistrust JJs in general? I kind of like their EL84 (but have EP14P in the AC10).
I notice that JJ make an EF806S which should be a special quality EF86. Never tried one, but I suspect the choice of such a prestigious name is a random marketing ploy
Great little amp. I loved the "do not use as a bass amp" sticker and then I saw the speaker... yeah that probably would be really bad to try to go too low with that tiny speaker.
The majority of valve amplifiers that I get in for repair have problems with JJ EL84s. The most common issue is the screen grid resistors burning up, caused by intermittent short circuits in the EL84s and that is not confined to just EL84s, a lot of EL34s suffer the same fate.
JJs don't seem to cope well when older.
JJ brought out an EL844 that was a disaster. It looks like a renamed Video Output valve from the PYE/Philips valve Colour TV days.
I know that JJ is a brand name but they do source from all over the World so I cannot tell where they were made by the time I see them burnt to a crisp.
I only dislike a product when it causes issues.
Hope that answers your query.
Thanks for that Jon. I was under the impression that JJ produced all their own valves at the factory in Slovakia, but I'm happy to be wrong - you see a lot more amps and valves than me
JJs get re-labelled by all the big brands of course (TAD, Ruby, Fender/Groove Tubes etc.). I have some Ruby EL84-Cz (very obviously JJs) that are over 20 years old and despite some discoloration still worked fine last time they were in use, but as noted above I have 6P14Ps in the Vox at the mo (y) .
How are the filter caps in the Selmer looking after a long soak?
The Slovakian JJs are lovely, as we would expect. I have a list of manufacturers and re badgers somewhere, when I find it, I will post it. There are now many Chinese manufacturers that are reasonable quality. Take the RS range of valves, not bad for budget valves. Their EF86s are a bit noisy though.
The Selmer has less than 180uA leakage in the smoothing capacitors in the single can and I am happy with it at full voltage. Possibly not far off the original specification.
So I pronounce the the capacitor healthy.
I reckon that this amplifier went wrong, caused by a very old and failing EL84. It was put to one side and then left for many years until it arrived here and now a new lease of life is planned.
I am checking the feed resistors and decoupling capacitors today, when I am happy with it, I shall power 'Sally' the Selmer up and ... watch this space.
A little bit of valve supplier info you may find interesting.
Shuguang is in China and is the second largest valve supplier. They make a good range of valves.
New Sensor Inc in New York, USA is the largest valve supplier. The company is better known as Electro Harmonix (EHX) . The manufacturing site is in Saratov, in Russia. The factory was purchased by the Electro Harmonix Group when the old Soviet Union became the Russian Federation. In Soviet times the factory was named Reflektor and made valves for the Russian consumer industry and the military. Today the production is mostly valves for consumer applications.
The Sovtek brand is effectively all the original Reflektor designs. EHX has bought valve designs and the license to manufacture popular valves from Mullard ( Philips), Tung Sol ( USA), Genalex (Marconi Osram), and also brands valves as Electro Harmonix. You don’t see Mullard new valves officially sold in the UK, because the European license only allows sales in Belgium. They are sold in the Far East and the Americas. Mullard valves for sales in the UK usually have been unofficially imported from another continent.
JJ Electronic, are based in Cadca in the Slovak Republic a smaller manufacturer making audio valves. JJ originally was the Tesla valve factory in the communist era. When communism vanished, the factory became a private enterprise and changed its name to JJ Electronic. Sometimes you see sellers advertising JJ Tesla valves for sale. No such brand exists today! It is either NOS from the Tesla days or new stock from JJ Electronic. Their valves are sold under the JJ brand however some companies buy them and re-brand JJ valves perhaps buying un-boxed ones and re-boxing them, others purchase cheaper valves and print JJ on them. Shame really because it spoils the good name of the name.
Source EMEA Semiconductor, UK.
Here it is, I knew I had a list somewhere. It is in my website; https://jonsnell.co.uk/page-5/page-13/
Thanks! That pretty much confirms what i believed, although I find a couple of points dubious, to downright worrying....
This is the most worrying and could be horribly detrimental to the JJ's reputation.
I'm sure New Sensor/EHX has a lot of money invested in marketing those premium brands, and maybe they incorporate some elements of the original designs compared to their inherited Soviet era designs, but a Sovtek Mullard ain't a Blackburn Mullard and a Sovtek Tung-Sol, while decent by modern production standards isn't the real deal either.
Of course, the article says nothing about New Sensor's treatment of Svetlana Electron Devices/SED/Winged C who were making great valves in St. Petersburg but seem to have given up entirely now faced with New Sensor's acquisition of their brand name and therefore their reputation in several markets, notably North America.
Also, the history of the Ei factory in Yugoslavia is interesting. How much was, or wasn't destroyed in the Balkan war? Did they or did they not have the original Telefunken ECC83 tooling? Was it all Western Electric's fault? The ECC83s of theirs that I have certainly resemble Telefunken and sound great.
Most 'fake' JJs are sold on fleabay!
A real worry for a genuine manufacturer.
Can't stop it as it is rife from so called NOS semiconductors to high end very expensive components.
When challenged, fleabay remove the seller but they re appear later, under a different name.
My golden rule is, if its cheap, its probably fake or the seller has no idea what is being sold.
SS rectifiers are excellent in a modern design that is looking for fast HT rise and low losses. If the amplifier has a thermionic rectifier, the 'sag' is part of the pleasing reproduction and of course Selenium rectifiers were very expensive and as hazardous as Mercury Vapour so for medium to high current Selenium was forgotten about.
I used to charge car batteries on my home made charger, it used a pair of 68506 mercury rectifiers to produce the required charge voltage. When the battery was low they would glow bright blue!
We have a working amplifier, just waiting for a new 'Tone' Pot with switch. The old switch has welded contacts and won't switch off.
There was always a little hum on these because they have no tank capacitor on the rectifier cathode. Fitting one of the correct value makes Sally sound even better with no detectable hum.
New cathode bypass capacitors fitted. Sally sounds lovely now.
This will rival any VOX AC4.