6G6gt in 6V6 circuits

[ALBATROS1234]

I was looking around for a low plate diss tube for a future project of low wattage Marshall type, was considering 6f6 and 6k6 types as they are true pentodes and thought perhaps characteristics might be more similar than a beam tetrode in Brit type circuits. I found the 6G6 type with 2.75 watt plate diss and thought this could be a possibility but cannot find much on them. They have 300vdc max on plates so that would have to be considered.  Has anyone experimented with this tube ? It is apparently an octal 6ak6. But 6aq5 is supposed to be a 7 pin 6v6 and they sound quite different. The 6g6 has a higher load resistance so an appropriate ot would have to be found. It's just an inquiry to see if any of you guys have any experience with this tube. All info appreciated.

[vampwizzard]

1) Double check pin out (i think they are the same.. 6v6 vs 6g6)
2) bias the new tubes within their working range
3) enjoy lower wattage output.

Most manufacturers will have a data sheet with the tube. Heres an old one thats probably safe for initial ballparking when you go to bias. Id also look at the blonde bassman amps that used those tubes.

http://www.r-type.org/pdfs/6g6g.pdf

[tubeswell]

The RCA datasheet has some suggested operating conditions, Including load resistance for running around 180 plate volts


https://frank.pocnet.net/sheets/049/6/6G6G.pdf




You could run it with higher plate voltages, but you would want to adjust load/screen voltage/bias etc

[PRR]

> You could run it with higher plate voltages, but you would want to adjust load/screen voltage/bias etc

Usually the datasheet conditions are about optimum. If you raise the voltage, you must decrease the current. This needs a higher load impedance. Since 180V 15mA already asks for 10K loading, we are getting up in the range where you can't get good treble response (with full bass). 300V wants 25K-30K load, and you only find that in very cheap audio.

Take the 150V-200V zone as target and work the rest of the amplifier to that. You do not need huge B+ on the driver because 6G6 at 180V needs much less grid drive than our bigger friends. You don't need huge B+ on the first stage if you control your gain so it won't fart before it gets to a gain knob.

[ALBATROS1234]

thanks gents for the replies, i do actually have the rca tube manual so i have the data sheet thats where i got the 300v max and 10k load imp. and its where i got the idea to use these tubes in the 1st place. so theres a bassman model which used 6g6 type tubes? i had not heard of this.

@prr this was helpful, i knew from other tube datasheets the load imp went up with increased voltage but had not accounted for it to more than double with doubled voltage(180v optimum to 300v max) nor did i know that load imp affects freq response in a meaningful way. it may be hard to find a push pull 5 to 10 watt ot to meet these parameters. i guess i am better off using 6K6 gt or maybe "G" type coke bottle types. its a noticeable volume drop from a 6v6 to 6k6 in single ended stuff and i have a couple rca 6k6gt that sound decent in 6v6 homebuilt type circuits.

[DummyLoad]

one tube i had considered in the past was the 6W6. a 10W anode dissipation tube that runs low-volt. a pair should make about 5-6 watts with in push-pull with a 8k-10Ka-a load.

it was attractive because for the PS, i would have made use of a pair of 12.6V/120V filament transformers back to back, with the 6V power tubes filaments in series and the preamp tubes at 12.6V. or just used the 12W6 with the filaments wired in parallel.

interesting that GE rates the tube at 7W limit anode dissipation and tung-sol rates anode dissipation at 10W - both ratings are in vert. deflection amp service.

--pete

EDIT: the 6CS5 looks like a 9pin version of the 6W6 

[ALBATROS1234]

that is strange that the same tube by diff manufacturers would have different values. doesnt that make them different tubes. thanks i will look at the 6w6. you know the drill want to get marshall tone without blowing the windows out and cant crank 6v6 pp without excessive volume thats why i was looking at the 6k6 with its 8.75w diss.figuring i might be able to get that down to 12 watts or so. so tempted to use a pair of these telefunken 7189s i got, i know though would some super duper but were back to blown out windows.

[tubeswell]

one tube i had considered in the past was the 6W6. a 10W anode dissipation tube that runs low-volt. a pair should make about 5-6 watts with in push-pull with a 8k-10Ka-a load.

I've run a 6F6 (11W tube) in an amp designed for a 6V6, and it worked out okay at around 340V. You just need to keep the bias a little cooler and the screens about 30V below the plates (because these have higher screen current)

[vampwizzard]

upon further review, the Blonde bassman's circuit was NAMED 6g6, and didnt have 6G6 tubes. Because thats not confusing.

[PRR]

> i knew from other tube datasheets the load imp went up with increased voltage but had not accounted for it to more than double with doubled voltage(180v optimum to 300v max)

In Audio service, especially small amplifiers (not 10,000W transmitter modulators), you normally design to hit the Plate Dissipation rating, because that is a major cost factor (6L6 costs more than 6V6, which costs more than 6G6) and you want all the power you paid for.

For the same power, if you double the voltage, you must cut current in half!

Resistance is V/I. 2X voltage and 1/2X current is 4X resistance.

> nor did i know that load imp affects freq response in a meaningful way.

Inductance, and leakage inductance, scale with number of turns. Since permeability of good iron is >1000, it is not hard to get 1000:1 bandwidth (20Hz-20KHz), if leakage inductance is the only limit. For audio purposes, 10 Ohms is great and 1K is not hard.

A big copper winding has capacitance. And this does not scale with number of turns, nominal impedance, but is all about the physical size of the winding. Say 100pFd-1000pFd for the lumps we use.

So as you design impedance higher, leakage inductance increases, capacitance stays the same. Eventually you have a upper resonance and no response beyond.

Also small transformers wound to very high impedance, large number of turns for decent bass response, get into many-many turns of very fine wire. Which has to be wound extra slow so it won't break. Ties-up the winding machine longer than a big low-Z transformer, and you pay for that machine and operator.

Even in the 1920s when Bell Labs was trying to develop a domestic loudspeaker, one of the first things they knew they needed to work on was "low Z tubes" which could make 1 Watt (their goal) without absurd voltages and high winding impedance. The best they could do at first was a type '10 working at 400V 18mA and 10K load. The 10K winding had to be sectioned to get enough bandwidth to show their cone speaker to best advantage. Within a decade we were using like 25L6 at more sensible 100V 50mA 2K load. A 2K winding is reasonably robust, easy to wind, and more than wideband enough for most audio.

There's no sin in working say 6V6 at 150V for few-Watt P-P output. You gain nice low impedances and long tube life.

[ALBATROS1234]

thanks guys, i appreciate the knowledge ,especially you p.r.r. i always learn from your responses. in this case you gave me an idea. perhaps i can use a isolation xfrmr to get a lower plate voltage on some 6.6 type and therefore get the volume i am looking for. i am excited to try some things and find out. one thing i was tossing around was single ended with a jtm 45 preamp. perhaps subbing a gain stage for the LTPPI and then i can use normal voltages and get 5 to 7 watt output. tubes are still a new thing for me although electronics are not, its made it way fun to be on this tone quest. thanks again gentlemen and happy holidays to all.

[DummyLoad]

thanks guys, i appreciate the knowledge ,especially you p.r.r. i always learn from your responses. in this case you gave me an idea. perhaps i can use a isolation xfrmr to get a lower plate voltage on some 6.6 type and therefore get the volume i am looking for. i am excited to try some things and find out. one thing i was tossing around was single ended with a jtm 45 preamp. perhaps subbing a gain stage for the LTPPI and then i can use normal voltages and get 5 to 7 watt output. tubes are still a new thing for me although electronics are not, its made it way fun to be on this tone quest. thanks again gentlemen and happy holidays to all.

then this thread may be of interest to you. 

from past experimentation, the plexi/bassman preamp does not sound as good with lower B+. a single tube SE or small-er tube P-P running upwards of 350V or more would probably work better. save the long life low volt approach for hi-fi unless your going to push low volt tubes to the edge. IMO and from prior experimentation, tubes in a musical instrument amplification application sound much better when pushed to the edge.   


--pete

[ALBATROS1234]

thank you sir i will check it out.

[ALBATROS1234]

i got the 6G6g nos rca that i ordered for test purposes. only 6.99 from world tube company. i popped it in my silvertone 8072 r2r amp which normaly uses a 6v6 at low voltage approx 200vdc on the plate so i figure this would work with the new tube. boy did it work great. sounds amazing almost as loud as the 6v6 which is odd since the 6v6 is 14watt pd and 6G6 is 2.75 pd. i understand power/volume is not linear and a 100watt is twice as loud as a 10watt etc but i expected more of a volume drop. fully cranked with both tubes the volume drop was hardly noticable. i imagine it has to do with tube spec differences and biasing of the circuit which this silvetone is grid biased with a 10k resistor to ground with the tone control between the bias resistor and ground which seems odd. i tryed to post a picture of the schematic but even after making it into a low res gif this site says "file too large" i will put a link below to a pdf of the silvertone service manual which has the schematic near the end.copy and paste the below link in your address bar of your browser and it will download the pdf to your download list .open that and click . cheers

sportsbil.com/other/Silvertone%208070,8072.pdf