6AV5GA triode strapped?

2nd harmonics for the masses

6AV5GA triode strapped?

Postby RobertWStephens » Mon Dec 03, 2007 7:35 am

Hello! I am gethering parts for my get*set*go and was wondering if I could use the 6AV5GA and triode strap them? I am just an assembler and read elsewhere that triode strapping this tube would give you a 6B4G equivalent. I am not sure if this applies to this project. I am trying to build it for under $400 without diminishing the design or sound quality. The 6AV5GA tubes are dirt cheap. Peace. Robert
RobertWStephens
 
Posts: 60
Joined: Thu Nov 30, 2006 11:47 am

Postby EWBrown » Mon Dec 03, 2007 7:58 am

I have experimented with 6AV5GAs in triode-strapped mode, and it indeed behaves very closely to a 6B4G, 2A3 (or 6A5). The screen grid G2 can be connected directly to the plate, or through a 100 to 1000 ohm, 2W resistor.

I set up a "bread board" circuit using an octal relay socket, and a Heathkit variable power supply and tried both fixed, and cathode (1K 10W WW) biasing, and the "static" idle current vs voltage results were quite close to those of a 6B4G or 2A3 ((I don't have any 6A5s to compare. This was a "static" test only and not a complete working amplifier so I cannot comment on sound quality.

(I thought that I had posted those results on this forum, but I can't find them, so maybe I forgot to Yellow_Light_Colorz_PDT_09 Yellow_Light_Colorz_PDT_02

(Apparently there is at least one tube vendor who sells re-based and triode-strapped 6AV5GAs as 6B4G equivalents).


These 6AV5GAs should work in the G*S*G cirucit, keep everything original 6AX5 tube rectiifier, (no SS diodes, please) and the RK for each can be either 1000 or 900 ohms, though I'd probaly err on the side of caution, initially, and use 1000 ohms. This can be later decreased to 900 ohms by paralleling 9.1K to 10K if desired). Even 1100-1200 ohms mightr be better, TBD... (see Shannon's reply)

I sent Shannon a MQ of "NIMB" (New In Moldy Boxes) Tung-Sol 6AV5GAs for future experimentation, a while ago, and he sent me a couple of GSG boards - one of which is now in a fully functioning and nice sounding 6B4G amp!

/ed B in NH
Last edited by EWBrown on Tue Dec 04, 2007 7:04 am, edited 1 time in total.
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Thanks Ed!

Postby RobertWStephens » Mon Dec 03, 2007 3:37 pm

Thanks Ed for your extremely thorough response! I will build mine with the 6AV5GA's. I can get a pair for about $12. You guys keep this fun! Peace. Robert
RobertWStephens
 
Posts: 60
Joined: Thu Nov 30, 2006 11:47 am

Postby Shannon Parks » Tue Dec 04, 2007 6:27 am

The Tungsols Ed gave me do behave very closely to a 6B4G. In my tests 1100 ohms worked better as a higher bias just made the distortion go higher. Even at 1100 ohms, they had a touch more distortion than the 6B4Gs. I didn't FFT the spectrum to see how the 2nd and 3rd harmonics compared, though, so I'm not sure of 'the sound'. A pair for $12 - you can't go wrong, right? Yellow_Light_Colorz_PDT_05
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby EWBrown » Tue Dec 04, 2007 7:03 am

A possible approach to reduce the distortion (and also the output power) is to use a 5K OPT primary. The James 6113s and 6115s already have a 5K tap, so it's a simply matter of trying either 5K or 3.5K and figuring out which sounds best.

The output power wll be around 2.5WPC @ 5K, and the distortion will be noticeably lower.

The 6AV5s don't need DC filament voltage, though it won't hurt to install it on the board. This way, it won't be a major project to later upgrade to 6B4G or 6A3 operation. The only changes would be at the chassis-mounted sockets, and if you use the terminal strips, this is an easily reversible / convertible process.

(FWIW, a 6EM7 is almost a half a 6SL7 and a 2A3 / 6B4G sharing the same jug. The PA section of the 6EM7 is limited to 10W max PD and 35 mA plate current, so it's not quite as powerful, at around 2W out, with a 5K OPT primary, though it can me pushed up to 2.5 to 2.8W with a lower B+ (275-280V) at 38-40 mA plate current - A 1K, 5W resistor is the ideal cathode resistor value for this combination).

A quick SE CAD using 6B4G and 325VDC B+, a 900 ohm RK and 50 mA plate current, and the James 6113HS or 6115HS OPT, shows the following:

3.5K primary: PO = 3.14W, 2nd = 4.7%, 3rd = 0.2%

5.0 K primary: PO = 2.55W, 2nd = 3.5%, 3rd = 0.1%


If RK is increased to 1K, plate crrent falls to 46 mA and the output power is slightly less and the distortion figures slightly higher.

/ed B in NH
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby Shannon Parks » Tue Dec 04, 2007 9:12 am

Good point, Ed. I think I neglected to look with the 5k taps. Something for me to look at!
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

SE CAD sez

Postby EWBrown » Wed Dec 05, 2007 12:18 pm

The G*S*G with the Magnequest RH-60 (5K, 60 mA, 30H, 185 ohms DCR) OPT and 350V B+, and 1K "cathode" resistor set at 51.2 mA gives some nice numbers: 3.2W @ 3.7 % 2nd harmonic, and unmeasurable 3rd harmonic!

The current crop of 2A3s is more rugged than the 60 year old "treasures", and the new J/J 2A3-40s are basically 2.5V 300Bs, so thay can be driven even harder!

I would SWAG that the larger jug 6AV5GAs can be pushed safely beyond 11 watts PD, at least 15W and maybe even more.

Continuous duty horizontal sweep and HV generation puts a heavy demand onn these tubes, and SET duty should be a "walk in the park" for them...

FWIW, These tubes also hav 12V and 25V filament versions, and the 6BQ6GTB and 6CU6 have identical operating characteristics, just with a different pinout and a plate cap. These also have 12V, 17V and 25V filament versions.

There may be other horiz sweep tubes that are similar. Time for some more reasearch.

/ed B in NH
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby Ty_Bower » Mon Feb 01, 2010 11:25 am

If I want to give this a try, where is the best place to connect the cathode? Should it go to J3-4, or J3-5, or TP1?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
User avatar
Ty_Bower
KT88
 
Posts: 1494
Joined: Wed Mar 21, 2007 2:50 pm
Location: Newark, DE

Postby EWBrown » Tue Feb 02, 2010 10:50 am

The 6AV5GA cathodes should be connected to TP1 and TP2 respectively (the top of the cathode resistor). DC filament voltage is optional - I'd use it, in order to eliminate any slight residual 60Hz hum

Connect G2 to the plate on each tube with a 100 ohm, 1W resistor.

This is all easily reversible should you later decide to use 6B4Gs.

HTH

/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby whitelabrat » Fri Jun 04, 2010 7:11 am

There are plenty of cheap *AV5's at ESRC. A compactron equivalent with a top cap is the *GV5. I've tried these and they to the trick. There are tons of possible sweeps tubes that may be usable. I'm currently tinkering with the 22KM6, but it has different capacitances so I'm not sure what effect that will have.

Have fun!
whitelabrat
 
Posts: 33
Joined: Thu Dec 20, 2007 11:37 am
Location: Maryland, USA

Clean Sweep

Postby EWBrown » Fri Jun 04, 2010 10:06 am

The 6GE5 is equivalent to the 6GV5, but with a different pinout and plate brought out on pin 7. 6GT5 is similar, but with a novar base.

There are plenty other sweep tubes which have similar characteristics. And as someone else here said a few years ago, they are "insanely" linear!

/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !


Return to get*set*go

Who is online

Users browsing this forum: No registered users and 12 guests