EL34 Pin 1 Ground?

[chunkitup]

I gutted a non functioning Traynor YBA-1a and built a JCM800 circuit in its place. My question is about the existing octal sockets. EL34 pin 1 needs to be grounded or does it? The sockets pin 1 is not there. The sockets were built that way. The amp originally came with 6ca7's.

[Jazz P Bass]

Well, that is confusing.
Without a Pin 1 connection (Grid 3) the 6CA7 tube was running as a Tetrode.
Or, the original tube was a 7027A & it was replaced by who knows who with a 6CA7.

Here is a write up on converting a YBA-1 that has 7027A tubes to an output with 6CA7 tubes.
(an external connection must be made from pin 1 to pin 8)

[chunkitup]

That amp came to me with GE 6CA7's which were used in this era amp and rectification was solid state. I just ordered new sockets to make it correct. I was just confused since all schematics for this amp show pin1 connection to ground.
Would lifting that ground create tube failure?

[Enzo]

It is the suppressor grid, no ground there would leave it floating.

[Jazz P Bass]

The YBA-1 originally (1966) had 7027A output tubes.
There was no connection to pin 1 because the connection was internal to the tube, Grid 3 & the Cathode, at pin 8.
Pin 4 (Grid #2) was internally tied to Pin 1.
http://frank.pocnet.net/sheets/049/7/7027A.pdf

So if the amp had 6CA7 tubes in it, either they where relabled beam tubes or the amp sounded like crap.
(there is a lot of confusion surrounding vintage 6CA7 tubes.)
Without a connection to Grid #3, the tube was running as a Tetrode.

[Leo_Gnardo]

So if the amp had 6CA7 tubes in it, either they where relabled beam tubes or the amp sounded like crap.
(there is a lot of confusion surrounding vintage 6CA7 tubes.)
Without a connection to Grid #3, the tube was running as a Tetrode.

Seen lots of EL34 (skinny bottle pentodes) marked 6CA7, plus 6CA7 (fat bottle beam tetrodes) marked EL34, plus both marked as both. Plenty of room for confusements. Plus tubes that were neither, marked as both, turned out to be beam tetrodes. Takes a second to ring out the connexion between pins 8 & 1 to see if it's there or not.

Back when I wasn't hip to it, tried EL34's in sockets that had no connexion to pin 3. I got power all right, sounded good too. Until the volume fizzled away after only 20 minutes and the EL34's were toast. To make it worse they were Siemens. Don't do like I did & make that misteak.

[chunkitup]

Whoops sorry! Everything is fine. They have pin 6 absent. All the octal sockets I have ever seen or used had all the pins and with pin 6 missing my thinking went straight to noval socket and the first pin after the gap is pin 1. I am really humbled on this mistake. I am an idiot.

[g1]

Thanks for clearing that up . Pin6 being absent makes much more sense.
Traynor used EL34 and 6CA7 interchangeably, whichever they had on hand at the time.
The sockets in the 7027 versions also had pins in pin1 position, whether wired or not.
The only way I could think pin 1 could have been missing was if someone had removed them from the sockets, but then the 6CA7's would not have worked right..

[Leo_Gnardo]

Whoops sorry! Everything is fine. They have pin 6 absent. All the octal sockets I have ever seen or used had all the pins and with pin 6 missing my thinking went straight to noval socket and the first pin after the gap is pin 1. I am really humbled on this mistake. I am an idiot.

Not to worry. If I don't make at least a mistake a day - I know I haven't done anything of consequence. Put dunce-cap on smiley thing here.

[daz]

I am an idiot.

I resemble that remark ! Just ask anyone here. Now gimmie it back !

[Chuck H]

I once spent an entire day to fix a new build. I had the layout wrong and the PI coupling cap was upstream of a load. Voltages didn't look bad and other readings in that circuit are confounded by the high input impedance. And somehow I just couldn't see the mistake on the board. I made myself put on the cap and sit in the corner.

Anyone else here ever burn a hole into one of those Lexan, touchpad face plates with their soldering iron?

The first time I designed a build with the first preamp tube close to the input jack (other side of the circuit board from typical) I had the cathode circuits flipped on the board. As a result I installed the bypass caps in reverse polarity.

I once soldered a power tube to it's socket because somehow solder managed to flow into the pin cup and weld the pin in place. Much harder to undo than to do incidentally.

Anyone ever decide to use an HD aluminum chassis, a plastic etch faceplate and then realize the seven standard Alpha pots they ordered don't have enough thread depth?

Here's one of my favorites! I once wedged a piece of automotive vacuum tubing between a warped fiber board and the chassis to stop a vibration problem. Turns out that stuff has enough carbon in it to act like a resistor! "Where's that smoke coming from!?!"

I could go all day.

[cyclone]

I had a radar system in the nav that had a 7 foot long travelling wave tube that put out .5 MW

The anode was at 55kv dc, the power supply had rectifiers the size of a golfball mounted to a water cooled manifold. The cooling water was purified by a deionizer so it was non conductive. One day when I was operating the radar under way, I got temp alarms. I ran down to the radar room, water was pouring out of the drawer with the rectifiers containing about 50 hv computer beer can caps and 55kvdc:0. I shut-er down quick. No arcing and sparking because I had faithfully done the pm's on the deionizer

A 3" piece of .25" ID fuel line (looking hose had popped, water filled the power supply but did not cause any problems!!

I went down to supply and got some fork truck fuel line hose, looked identical. Short story, the hose arced due to carbon content and dumped 10 gal of water into the HV supply. Again. Still no problems. Ordered some orange (butyl) rubber hose , dried out the drawer, fired her up.

That TWT went down in transconductance during my time on the ship and I replaced it, there was a chainfall above the tube to lift it)) Good times