Low wattage amps using 7 pin pentodes

[RJ Guitars]

Hello all,

I've monitored the site for a while but this is my first post... I am delighted to have found this forum.

I've searched for a few years for great tone in small packages. I've had some success using a variety of 7 pin output tubes such as 6AK6, 9001, 6AK5, 6AQ5, 6AN5, 6AG6, 6AU6...etc.. there are a lot of choices and they are pretty easy to find as well as very cheap.

I've built a nice SE champ style amp and also a great little push pull... but I know there is more that could be done.

Has anyone else experimented with these tubes or have any comments on them?

rj

[unklmickey]

if you want very low power and an extremely compact package, you could ues a 12AU7 for the output.

either one or both triodes (in parallel) for a SE output, OR both triodes in push-pull.

[RJ Guitars]

I've got one amp that is a PP triode output and it works quite well. It uses a 6SN7 octal for the power tube. I've got another in the works that I plan to use either a 12BH7 or an ECC99 for the output tube.

The hope in starting this thread is to find any builders working with or interested in some of those really small low output 7 pin pentodes... some of which are actually similar to some common Octals. As an interesting side note, they are easy to find in vintage NOS condition and are generally pretty cheap too... just not in major production quantities.

I believe it is the 6AQ5 that shares similar specs to a 6V6... but has a lower max voltage.

Some of those other tubes I mentioned earlier have a lower output wattage and in my limited experience they seem like good candidates for a lower output "Carmen Ghia" type circuit... or perhaps could they contribute to a new Dumble Xtra-lite clone?

Just looking for someone else who has built something with them...

[tubetek]

+1 for the 6AQ5W/6005
I've built a few Champ-type SE amps using the 6AQ5 type and have been
impressed. My current fave is the GE 5 Star MilSpec 6005/6AQ5W.
And talk about cheap; I bought some from www.radiodaze.com and had a selection of NOS brands for $4.75 to $5.00US per tube.
I think that these sound (within their limitations) on par with all NOS 6V6
I've compared them with...Try buying NOS 6V6 for $5.00!!
tubetek

[klingo]

shhhhhuttt!
don't speak too loud of our CSF 6005, or they will disappear as their MAZDA & VISSEAUX big brother

[RJ Guitars]

Lately, I've tried an EL-95 in my 6AQ5 champ circuit... and it's quite nice. These things are again very cheap and relatively plentiful... kinda in that magic spot where they aren't common enough for the big companies to use them, but plentiful enough that the price is good for the small time home builder crowd...

I've posted this elsewhere but I thinks it's good stuff... there are many great sounding low output 7 pin pentodes that will swap in and out with no mod or very minimal work... some of them sound way cool on top of being cheap...

rj

[krash]

Speaking of ECC99, I have tried one in a Serena. That tube is packing some heat, for a little tube. I bet a Serena makes 5 watts with an ECC99 and 300+V plates.

Anyway, even though it works and it's loud, it really doesn't sound that great for distortion tone IMHO. I really prefer a 12AU7 or 12AT7.

Back to your normally-scheduled pentode talk...

[RJ Guitars]

Thanks Josh,

I've listened to your Serena clips and I think the "High Voltage" clip has stellar tone and guitar work... which output tube was that?

I've got a 9 pin PP triode amp in the works right now that was somewhat inspired by your Serena amp...

I also have a 6SN7 PP amp that gets some really sweet distortion, but it's not very loud. My main gig is at church and on a few occasions I find I need to send a little bit of signal to a 2nd amp if I need a big clean tone... and we don't play loud.

Also I play a Les Paul Standard and I just don't get any feedback even with everything cranked full out... do you get feedback with the Serena... if so, is it the amp or do you use a lively guitar?

Finally, have you ever messed with the low wattage 7 pin pentodes? I like'em...

rj

[klingo]

krash wrote:Speaking of ECC99, I have tried one in a Serena.........

i want to try these also ,which OT impedance have you applied to the ecc99?
i was thinking of 320v/14Kohm for 1 tube/dual triode....and my crappy blues jr OT for 2 tubes/doublepushpull.

[krash]

Thanks Josh,

I've listened to your Serena clips and I think the "High Voltage" clip has stellar tone and guitar work... which output tube was that?

thanks for the props. That's a JAN Philips 12AT7. A 12AU7 (new JJ) sounds better IMHO, across the board. The 12AT7 is just barely hanging on at the Serena's plate voltage and will red plate if you run it hard for like an hour or more.

Also I play a Les Paul Standard and I just don't get any feedback even with everything cranked full out... do you get feedback with the Serena... if so, is it the amp or do you use a lively guitar?

It's the amp! Well I don't know, it gets that kind of feedback with all of my guitars, including:

Fender Esprit with DiMarzio PAFs (8.2ish K pickups)
Turser SG clone with DiMarzio & mongrel PAFs (7.5ish K pickups)
MIM Telecaster with Duncan broadcaster/classic-tele pickups (7ish K pickups)
MIM strat with Fender 57/62s (5.6ish K pickups)

The key to getting feedback on demand like that is in the amp voicing, and I guess to some extent maybe playing technique. However, really it just pops out of a Serena. You gotta build it right bro.

Finally, have you ever messed with the low wattage 7 pin pentodes? I like'em...

rj

Nope. Kind of wanted to focus on common, easy to get tubes for my production amps.

[krash]

krash wrote:Speaking of ECC99, I have tried one in a Serena.........

i want to try these also ,which OT impedance have you applied to the ecc99?
i was thinking of 320v/14Kohm for 1 tube/dual triode....and my crappy blues jr OT for 2 tubes/doublepushpull.

8K OT impedance

I suppose your Blues Jr. transformer will work. I am probably running close to 320 V plates in a Serena. For dual parallel triode SE I'd think you'd want lower like 4-6K. The plate res. is like 8K or 10K IIRC... look at the data sheet.

A 12AU7 is about 3-4 dB quieter but sounds a lot better to me!

[RJ Guitars]

Josh, Thanks for the notes... I agree the 7 pin stuff is probably just for the casual home builders. I can always find a few of anything, but I spose that when you need a guarantee of consistent supply in larger quantities it's not gonna happen.

concerning your other notes... 320 volts on the plates of the Serena... I wouldn't have guessed it to be that high... but I can't argue with that tone!

I was planning to use a Hammond 269EX on my next Push-Pull triode. It makes 180 AC so I'll max out around 250 or so... now you've got me thinkin' I want to wind it up a little tighter...

rj

[krash]

well the plate voltage depends on the tube choice. It's cathode-biased and has some voltage dropping here and there but with no tubes in it it's over 320 and even tho I haven't measured it with all differeent tubes, I think it's likely hovering around 300V most of the time.

Of course also to get the PI and the preamp to work right you gotta have a rail at 265V+ so might as well go for the gusto. I don't think a lot of folks are going to be whining at me for short tube life when you can retube the entire output stage for under $10 and put a NOS tube in it for $20. Heck the main cause of short tube life is that you just can't stop playing the thing.

[RJ Guitars]

Josh,

Thanks again for the note... I apologize because I don't follow the lingo right on the money... when you say you've got to have a rail at 265V for the PI... I understand that PI is the phase inverter, is the 265v rail the voltage tap for the PI tube?

If that's the case I guess that is a bit higher than normal.

rj

[krash]

yes that's right, that's about where the plate voltage is for the PI. Other downstream preamp tubes are close to 200V.

I think these amps sound good with high voltages. However some folks have good results with power scaling so YMMV I suppose.