6aq5 to el84 converter

[matt h]

(deleted)

[The Ballzz]

matt h,
Thanks for adding to the "wisdom" already shared. I'm in agreement with you, and was thinking much the same, which is why I brought up the point about the 365v. Just making sure that you hadn't missed the use of EL84's!

To your point about marketing/watts/etc, I'll add that it is my considered opinion that most people make too much of a big deal about wattage ratings. The important thing is for an amp to sound great and do it at the intended volume/sound pressure level, WATTS BE DAMNED! I've heard and used 5-10 watt amps that absolutely can cut through the mix and certainly heard (well, actually NOT heard) other 20-35 watt amps used in the same situation that simply get buried!

And then there's the issue of the equation of $$$ vs watts! What a joke. Except for the iron and a few other small factors, it costs just as much to build a "GOOD" low wattage amp as a higher wattage amp with the same features and quality!

My $.02,
Gene

[billyoung]

i just got some 68 volt do-5 zeners might tame the jca22h so can use the adapter we have been discussing I also been looking at the russian EL90/6p1pev on flea bay. the price seems good wonder if the will run higher voltages ?

http://www.ebay.com/itm/6AQ5-EL90-6P1P- ... 258a93692b

[guitar-rocker]

Those 6P1P's, while similar, are not a direct replacement for a 6AQ5/EL90, although they share a lot of same qualities. Please note that they are 9 pin also.

And dumping a lot of voltage via a DO will result in a large amount of heat issues to deal with. You would want to think through how to best handle placement of the heat sink needed and the surrounding heat that would come with it.

[billyoung]

have you used them ?

how are they tone wise compared to 6v6 and el84 ?

trying to get away from el84 bite.

[guitar-rocker]

I have not tried the 6P1P's, but have built several amps with the 6AQ5's

[The Ballzz]

billyoung,
I'll pose a set of questions for you:

A) What makes you so certain that it is the EL84 that is making the sound you don't like? It seems the only way to be sure would be to rebuild the power section of any given amp, with all the preamp, etc. (including voltages) identical, to accommodate/use first one power tube and then another.

B) Is it possible that every amp you've tried with EL84's might just be a poor sounding amp because of all the rest of the topography and design?

C) While I certainly understand that the power amp section can have a large effect on the overall "character of an amp (especially one that is regularly driven/pushed to it's limits), an awful lot happens in the preamp section!

And, FWIW, many of guitar-rocker's amps are built around cathode biased 6AQ5's and sound ABSOLUTELY AMAZING! Of course a lot of that is likely due to his stellar build quality and attention to minute details! His 6V6 and EL84 models ain't too shabby either!

Just Sayin'
Gene

[JMFahey]

Just curious, is there any magical quality attached to 6AQ5 which is missing from EL84?
Besides the obvious power capability, that is.

90% of the sound in an amp is in the project, how things are set up and matched to others, maybe 10% can be attributed to parts themselves.

Of course parts vendors say exactly the opposite for obvious reasons

I'm talking electronic parts here, not "mechanicals" such as speakers or ëlectromagnetic" ones such as transformers.

I fear some are comparing apples to oranges: they dislike their current 12AX7/EL84 based amplifier, with modern largish (at least adequate) transformers driving a modern speaker (even "reissues:" and "repros" are modern by definition) , so far so good, taste is taste, then plug their guitar in an old crummy 50's "2W practice amp" , single ended, poorly fed and filtered, driving a crummy and by now moth eaten speaker through a ludicrous transformer and LOVES it.
So far, fine.

So he reaches behind , sees a skinny 6AQ5 and thinks : "so there's where the Magic lives, I'll plug one (or two) in the amp I hate and it'll become like this one" .
Sorry but it does not work that way.

You want the *old/small/lo fi* sound?
Fine, I couldn't agree more (in fact I do have one such widowmaker which I properly converted with an isolation transformer and grounded 3 leg power plug) which sounds glorious ... but it was born that way.

If you love that sound, I suggest you buy some old radio at Salvation Army or similar and build one yourself (with the added safety options, of course).

Bonus: you have the old radio speaker to play with

[The Ballzz]

JMFahey,
Tonal/breakup characteristics of the 6AQ5 lie somewhere between EL84 and 6V6 with a little bit of the character of a 6L6. Pretty cool sounding tubes, when overdriven & thrashed like a red-headed step child!
Gene

[billyoung]

i had a marshall plexi combo and did not like it tone wise

i had a 71 50 watt laydown main was the best tone i heard , so

i am pretty sure i dont like el84s

[billyoung]

i FOUND THIS:

" i've built several amps using 6aq5's and run them in the 400 -420v range no problems---some have been in use now for 7-8 yrs without a peep. the latest 4 amps i've built using them have been a z-28 circuit running around the 380v - 385v mark on the plates and screens. these are gigged on a regular basis and no problems yet. these tubes are a lot tougher than tube manal specs allow for, like most tubes we use. a 250-0-250 @125 -150ma trannie would be just fine. you'd end up with about 330v on the plates which is a nicely conservative operational place for these. rh "




Guess like other tubes will handle alot more.

[guitar-rocker]

I would have to say something in that story appears to be incorrect. There is no way a person could run the 6AQ5 long term at 380v-385v on the plates (the data sheet says 250 max plate voltage). The internal mechanical construction of the tube has the plate laying right next to the glass, and several people have reported burning holes through the glass from red plating.

[billyoung]

i know some tweed champs have such high voltages techs are afraid to work on them.(well over 400) Have to run USA made tubes and pray alot. Some are owned by studios for recording, techs hate to work on them,If it has a meltdown while being repaired they will be blamed, and some probably have crusty transformers to begin with.

I know a sovtek 6v6 shorts in 400 range but say a tung sol will do alot better.

Heres the thread from this forum

https://tubeamparchive.com/viewtopic.ph ... n+400+420v

Someone suggested russian version but its data sheet says same for voltage.

Lots of amps run power tubes over maximum safe limits and many say the ones that do sound best, I have heard alot of good sounding amps with tubes that ran on sensible voltages.

I think when i have time will see about dropping the voltage in the jca22h
seems stupid high to me. I know marshall had trouble on the 18 watt series burning up.

[guitar-rocker]

While I have been personally responsible for taxing some other power tubed amps above their rated data sheet values, and they have taken the abuse, why go through all the trouble of reworking an amp to end up having it be pushed beyond design limits. You might want to consider another PT choice to enable you to get your rework build to a much more manageable state. The MPS 275.2 is a reasonable cost PT, with 275-0-275v CT, or the ClassicTone 40-18085

[billyoung]

heres another guy :

"all the info with voltages are on the updated schematic taken using a variac set at 120vac. I have it biased at around 26ma/70%. filaments are running around 6.5vac. the 6aq5's are running 325vdc on the plates, I think they are only rated for 285. But hey if we can run 6v6's and el84's at over 400 I should be OK

it's a little beast."

seems like it might be worth just making and trying an adapter, has anyone encountered a schematic or would just pin translation be ok ?