Tube Rolling w/Crack

[rlyach]

I received the Mullard 6AS7 in the mail today. Here it is next to a classic RCA 6AS7. The Mullard bottle is larger, the cooling fins are different, and the getters are different. The actual plates look the same however.

[ffivaz]

Your Mullard really looks like a rebranded Svetlana. I have one that states "Made in West Germany" (no other brand). If I'm not mistaken, I would say they were all made in Russia. IMHO, the big (at least bigger than my RCA 6AS7Gs) metallic deposit at the bottom of the tube is a good indication of Svetlana.

[rlyach]

Fabien,

I believe you are correct. Here is a Svetlana tube. Looks identical. I hope it sounds good.

[lordnikon]

Does anyone know where I can buy GEC 6AS7G online? I know they're hard to find and there aren't any on eBay either.

I've only managed to find an NOS GEC 6080W selling for $75US. Reasonable?

[JamieMcC]

There are 4 or 5 on ebay at the moment search for A1834 or CV2523 instead they can come branded as GEC, Osram, MARCONI, MOV & Genalex they are all essentially the same 6AS7G tube from the same factory and can be identified by the silver saucer shaped cup getter at the base of the tube. You will also find unbranded government issue ones with just the identification numbers on them. Some of the early MOV ones have black bases but the tube structure is the same.

[ffivaz]

I had good experiences with Langrex in the UK (Ebay or langrex.co.uk). They have some GE 6AS7GA for 12 £. I never heard of the this tube before but I just ordered one, the bottle is something between a 6AS7G and a 6080

[Bamboo5354]

Can anyone tell me if this is the same as the GEC Brown Base 6AS7G A1834 CV2523? About to pull the trigger.
newbielink:http://www.ebay.com/itm/6AS7G-A1834-CV2523-TUBE-GEC-OSRAM-MOV-BROWN-BASE-/121325981859?pt=UK_Sound_Vision_Valves_Vacuum_Tubes&hash=item1c3f9790a3 [nonactive]

[Loon]

Yep.  Jamie on the forums here has listed this one.

[Loon]

Anyone tried a 13D3 in input position?  Looks like a higher gain version of 12AU7, just as ECC32 is a higher gain version of 6SN7.

[Paul Birkeland]

The 13D3 will give higher than desirable grid bias on the 6080, so not the greatest idea without modifications.

[Loon]

Thanks Paul.

Don't mind modding to get a good op.  Experimenting is half the fun! 

I guess I draw a load line on the data sheet, find the 75 V Plate voltage and either use Ohm's law to determine the necessary plate load and/or change the tube's grid voltage using a different LED to set bias.  Do I have it right?

[Paul Birkeland]

Draw a dot at about 75V and 1.5V of cathode voltage.  If you have the Speedball, you slide over to the "Y" axis and look at what current this is, then set R1 appropriately.

If you want to use resistive plate loads, add a dot at maximum voltage (power supply is about 200V, so use that), then connect the dots, drawing your line till it hits the Y axis. The slope of this line will be the plate load that should yield 75V.  Do note that this doesn't assure good performance in terms of distortion, just that you get the voltage you need. 

[Loon]

Cathode voltage?  Do you mean grid voltage?

[Paul Birkeland]

It is grid to cathode voltage, so 1.5V on the cathode is considered -1.5V on the grid (provided the grid is grounded of course).

[Loon]

Awesome.  Thanks for clearing that up. 

Is there any reason to suspect distortion!  Can I predict this in advance from the data sheets?

Thanks