Mullard/Valvo ecc83 question

I've got some Valvo EL84s in a guitar amp, and a nice little pile of Mullard ecc83s... I haven't A/B'd Valvo (12ax7s) with Mullards, weren't those factories all setup by Philips?. I have messed around quite a bit with old preamp tubes, and I think most all of the old stuff is good or better than good. Mullards have a little more mid to my ears than the US stuff. Lately I'm really diggin Amperex, and Sylvanias, but it's all just different flavors, and there's lots of good old tubes. Your best bet would be to try to make some good buys, and then do a bunch of swapping in that preamp.
12AZ7s and 12AV7s are mostly under the radar, they're similar gain to a 12AT7, but many people don't know that a 12AZ7 or 12AV7 will swap in for a 12ax7 with only somewhat less gain (about halfway between a 12au7 and a 12ax7). Those can be found for cheap and can sound great.
Eventually you're going to need a tube tester, then the whole world of used tubes opens up to you. Used tubes can have thousands of hours left on them, don't be scared of used, - more and more I think NOS really means "tests as new, cosmetically new" anyway.

 

I used to buy used tubes from this guy back when they were more affordable:
http://www.audiotubes.com/
This site is still a good source for information on used and NOS tubes.

 

Find yourself a good tube substitution manual. It will tell you of "industrial" type and military type tubes that are excellent subs for ECC83 and whichever else type of tube. It will also have diagrams of the bases each type uses. Pay attention to that. Two tubes may have identical electronic charicteristics, but have a different pin configuaration. Any tube listed as a direct sub would have the same pin configuration however.

 

You may also try the "higher end" 12AX7 tubes from the 50's and 60's selling on eBay. There is a difference that you can really hear, particularly in hybrids like SWR that only take one to three 12AX7 tubes. It can get a bit risky with vintage gear, but if you stick to sellers with 98+ feedback that post tube tester measurements, you may get a much better deal that from Brent Jesse. Here's what to look for, IMO:

1) For all round balanced performance on the mid-rangy side and nice shimmer: Phillips (Amperex, Bugle Boy) tubes branded with three or four digit date codes, all beginning with a Delta symbol for the Heerlen, Holland plant. The three digit tubes are from the '50s; the four digit tubes are from the '60's - the number following the delta is the last digit of the year, and the third digit is the letter corresponding to the month (A=Jan, B=Feb, etc). Look particularly for the 17mm long plate tubes with foil D-getters and copper grid posts, or the triple-mica Phillips SQ tubes. Expect to pay $80 - $125 for the Bugle Boy D-getter tubes, and $40 - $80 for the long plate Halo, or round getter tubes with copper grid posts. Short plate 14 mm halo getter Bugle Boy tubes go for $30 - $50.

2) For a warmer tone than the Dutch tubes, but also a lot of presence and mid-range: Mullard tubes branded with three or four digit date codes from the 50's and 60's (like the above) beginning either with a B for the Blackburn, England plant, or an R for the Mitcham plant. Look particularly for the box plate CV4004 or M8137 tubes, and the long-plate square or D-getter tubes with copper grid posts. Expect to pay $80 - $125 for the square getter tubes, and $60 - $100 for the box plate tubes. Long plate halo getter tubes with copper grid posts go for $50 - $100, and the 14mm short plate tubes $40 - $80. The gold colored shield 14mm plate tubes appear to have a higher gain than the white shield Mullards at the same price; and the 10M tubes (10,000 hour life) tubes with 14mm plates go for $100 - $200 per tube, depending on the condition.

3) For even and accurate tone and linear presentation: Telefunken, Siemens and Valvo tubes. The date and manufacturing codes are confusing with the Telefunken tubes - but look for Siemens and Valvo tubes that have date codes beginning with a D for the Hamburg plant, or the vertical ++ symbol for the Munich plant. Telefunken tubes should have a diamond or square shape <> embossed in the bottom glass. The tubes will always have a halo getter, but look for the 17mm long plate tubes. Valvo tubes may have a halo getter welded to the plates at a 45 degree angle, which is highly sought after. Expect to pay $40 - $80 for the most German tubes, and the sloped halo getter Valvos go for $80 - $120. The Telefunken ECC803S is possibly the longest lasting 12AX7, and goes for $300 - $800, depending on the condition.

Some note on the condition of tubes:

1) Collectors in Asia pay a premium price for tubes with clear and pretty silk-screened logos. These easily wear off. That means you can get high-performance tubes with faint or even no logos at really bargain prices. Expect to pay on the lower end of the rages above for a no-logo tube.

2) Look for high mutual conductance test readings if possible. The seller should provide readings for each of the two tube triodes, and the closer they are together, the better the tube will perform. Also the higher the values, the better the condition is and life expectancy of the tube will be. Make sure the seller divulges what the reference values are with his tester, for either a good or a new tube. Be suspicious of a used tube from the '50's tests "better than NOS" (new Old Stock). That seller is most likely either not using the tester correctly, using a poorly calibrated tester, or is outright lying. Now, I have a Hickok 800 that I can set up so that a reading of 1250 Micromhos is an average new tube; but I can also set the tester up so that 1250 is a minimum good reading. A tube that measures over 1000 on each triode, when set up for 1250 = new, is a pretty strong tube. That same tube will read 1900 or better, when the tester is set up for 1250 = minimum good.

Well now you have my tube spiel. I hope I wasn't too boring. Happy tube hunting!

 

At the cost of being boorish, may I suggest that you wait and actually try the amplifier before making plans to modify it. At this time you do not even know how it sounds let alone what it would need to "fix" it. Live with the beast a while, you might even like it as it is.

Paul

 

THe V1 or first valve in the preamp, along with the driver tube, the tube socket that is usually closest to to the power tube section are the places that you need to spend your money on, besides choosing the right set of matched power tubes. A good balanced Mullard or Telefunken in the V1 spot in terms of an ECC83/12AX7 tube are both excellent choices if thats the tube type you want in the V1 spot. I also advise searching the net for all of the web sites put up by tube amp geeks to help you get a lot of great tips on how to get the response you want out of your amp with just choosing the right tubes.
The other aspect is that with new power tubes get them biased by a tech if you should swap them out. I wish you the best on the Trace Elliott head you are getting.