6AQ5's

[whitelabrat]

Anyone consider the use of 6AQ5's (EL90) tubes instead of 6BQ5 (EL84) tubes? I can wire the 7 pin sockets into the 9 pin holes. I would figure that the bias and voltage requirement would need to be adjusted appropriately.

[TomMcNally]

I dunno .... I think of 6AQ5's as low-budget 6BQ5's ... and with the low prices of 6BQ5's these days ... there isn't much benefit in my mind.

[whitelabrat]

The 6AQ5 is not a top performer as far as power output is concerned, but supposedly it sounds better than the 6BQ5 if you can sacrifice a couple watts. I can't say, cause it's only hearsay to me. They're real sleepers though as far as pricing is concerned. For example a quad of new EL84 would run about $30-$40 plus shipping. A quintet of NOS JAN 6AQ5's can be had for $10 plus shipping. Show me a quad of NOS EL84 tubes that are inexpensive?

I've heard rumors that 6AQ5's can be used with the Dynaco ST35 and I find that enticing. The voltage ratings are less than the 6BQ5, and the pinout is different, but otherwise they're very similar.

[TomMcNally]

I've seen the no-name Russian 6BQ5's in the $ 15 per quad range, but I don't know how good they are. I have some someplace, I should give them a try. Well ... go for it ... give us a report. It seems like a lot of work to wire up 4 off-board sockets. One of the advantages of a printed circuit board is that it's all one piece.

[EWBrown]

6AQ5s / 6005s will deliver around 10 watts PP, the OPT primary should be 8K to 10K a-a, and the B+ will have to be lowered to 300VDC or less.
They will work in Ultralinear mode just fine.

I recently built one of the new S-5 brand 16WPC 6005 / 5670 PPP amp kits, and it sounds pretty doggone good, even with the cheapo supplied PP iron. This amp runs around 230V B+, and around 24-25 mA cathode current for each tube, which is running them real "nice and easy". 16WPC is a bit of "creative optimimism" , as the "numbers" work out closer to 12WPC max , before the sound starts getting a bit raggedy... Yellow_Light_Colorz_PDT_02

NOS JAN 6005s and JAN 5670s are in plentiful and cheap supply.

The 5670 is a small dual triode, with the same characteristics as 2C51 and WE 396A. Totally different pinout than 12AX7 and its siblings.

Yeah, I tried some WE396As in this amp, they are nice, but they really deserve better OPTs to gain the maximum sonic benefit.

6AQ5s are basically 6V6s, in smaller glass packages, with somewhat less plate dissipation and maximum power capability. but the basic operating paramaters are nearly identical, as are 12AB5s..

I've read of some of the old metal shell 6V6s, actually containing an octal to seven pin adaptor, and a 6AQ5 hidden inside. :o Just like a box of chocolates, you never know what you're gonna get... Yellow_Light_Colorz_PDT_09 Yellow_Light_Colorz_PDT_05

/ed B in NH

[whitelabrat]

A side question regarding the resistor pots on the ST35 revD board. Can I mount them on the top or the bottom of the board... or both? I would expect some polarity from the part's datasheet, but I can't tell from the ST35 assembly instructions.

[whitelabrat]

It may be time for me to revisit this idea. I've got a spare 270HX transformer that should be able to provide 300v B+. I figure I can skywire in sockets underneath the noval sockets so I can easily switch back to 6BQ5's down the road.

Some resistor adjustment may be needed to be sure the driver tubes get the voltage they need.

We'll see.