is a triode a triode etc.

[ALBATROS1234]

i just purchased a 16 tube "lot" for experimentation and a learning tool, they were quite cheap so i figured why not. my ultimate goal is to learn as well as design and repair guitar amps. my question seems simple but it may be more complicated than i realize. what makes a triode or any tube more suitable for one purpose or another. in other words is a hi mu dual triode not basically just that.


 in my trusty rca recieving manual if i look up one it says mainly used for af amps, others with similar spec are said to be used as rf  or if amps or even verticle deflection amplifiers etc. can i not use these tubes for audio? if not why? other than possible higher noise to signal ratio or different optimum frequency ranges what is essentially the difference? can i not graft any triode or dual triode into an existing schematic as long as i pay attention to its needs and outputs changing values of resistors and caps as needed etc. included was a pair of nos 6f6 which it seems i can use as output tubes and a 5w4 recto i think i can use. but i have a couple tubes that seem like i may be able to play with esspeciallt a pair of nos 7f7 loctal hi mu dual triode and a threesome of 6sj7 pentodes that i would like to experiment with,but what does sharp cutoff mean.


i am sorry if these are annoying questions that have perhaps been asked, i just naturally question things and want to know why these terms change the game of amp design. why does everyone seem to mainly use 12a-7 family tubes for preamp when there seems to be many that would work fine. also why must most guitar amps use 6v6,6l6 types or el34/84 types. do other tubes of similar design just sound like shite? trying to learn the basics of tube amplifier design at this point any and all fact or opinions welcome. thank you

[66Strat]

If you can't find the data in the manual that you have, the tubes were likely considered obsolete at the time the manual was published. My suggestion would be to make a listing of the tubes that you have and cross-reference the listing to an older copy of the RCA Receiving tube Manual. RC15 would be a good start. You can find the manuals at the following link. http://www.tubebooks.org/tube_data.htm The 6F6 tube operating parameters are reflected on page 109 of RC15.

[shooter]

might surf up tube design, theory, and operation, to "understand" why an RF tube is really good for RF but sucks for AF, but like you said, for learning n experimenting, so get your breadboard set up and play. 

[silverfox]

Suitability of various Triodes.

There are numerous considerations, here are some. A tube has a particular capacitance associated with the internal structure. That capacitive value may interact with the external circuit components, with the result that what you desired as the outcome is either skewed or unobtainable. The tube itself may cause the circuit to oscillate.

Tubes have various power ratings as do resistors and other components. So if you try to pass a large signal through a low power tube it becomes more like a light bulb- For a brief period of time.

The amount of power needed to turn the tube on or off is determined by the design.

High frequency vs. low frequency: As mentioned previously, design of the tube limits the frequencies that can be passed through the tube. RF will find a way to take the shortest or possibly a unanticipated and more complex route through the tube causing signals to appear where it was not expected.

These are some of the limitations.

Depending on your area and the future of tube amplification, you will be farther ahead if your in this journey, and it is a long complicated one, in this journey for other than economic benefit. In my area, there really isn't much of a market for tube anything. Having said that, my personal experiences with taking up tube electronics later in life have benefited me by getting my dated electronic assembly and troubleshooting skills back up to speed. Keeps the mind active. Money? No. Your mileage may vary. Have fun, don't get a shock!

silverfox.

[ALBATROS1234]

i have the tube data , to simplify im wondering what makes 2 hi mu dual triodes different when in the data they look quite similar but in the descriptions of usage one says primarily used as af resistance coupling amps and another says used as rf or if amps.i get that rf is radio freq which is a higher range and if is intermediate but it seems like if i put af on the grid would it not amplify that input? for instance maybe it sounds thinish so couldnt i change values for plate and kathode resistors/caps to compensate or is this a pure waste of time and using a certain triode will sound like crapola no matter what or is the 12ax7,at7 etc preamp tubes just something amp designers use because its familiar? i want to know can i break or bend traditional rules of thumb and get a decent result?

[ALBATROS1234]

thanks silverfox was typing as you posted. im not doing it for money ,i have a job as an union electrician but i used to repair electronics and have always been into tweaking and modification of things, in short im doing it for personal adventure and desire to experiment with tonal textures vacuum tubes are something i havent fooled with much, the limits being i used to assist another biomed tech when working on x-ray equipment 15 years ago. i am really just wanting to know why cant i used this one or that one in place of similar(on paper) tubes.

[92Volts]

12A_7 tubes have been continuously available and will be in the foreseeable future. A common pinout makes design and minor changes to the design easier. Customers are familiar with them... and like the ability to switch a 12AU7 in place of a 12AX7 for less gain (whether or not the amp was meant for this!)

RF tubes can be used for audio. 12AT7 was originally for RF. It's now common in audio/guitar, considered interchangeable with the 12AX7/12AU7 (to some extent) though this wasn't why it was developed.

You usually don't want RF amplified as it's a source of noise. Also, microphonics could be a problem at audio frequency that radio tubes might not have been designed to avoid...

I'd say the biggest reason "oddball" tubes aren't popular is if your specimen dies, you need to rewire/redesign for the next tube you have. Or buy a replacement on eBay, not your local guitar shop. You probably couldn't get 20,000 so you're not mass-producing an amp using them-- it would be impractical for you and for your customers.

None of this means designing a one-off amp to use them isn't possible.

[92Volts]

i have the tube data , to simplify im wondering what makes 2 hi mu dual triodes different when in the data they look quite similar but in the descriptions of usage one says primarily used as af resistance coupling amps and another says used as rf or if amps.i get that rf is radio freq which is a higher range and if is intermediate but it seems like if i put af on the grid would it not amplify that input? for instance maybe it sounds thinish so couldnt i change values for plate and kathode resistors/caps to compensate or is this a pure waste of time and using a certain triode will sound like crapola no matter what or is the 12ax7,at7 etc preamp tubes just something amp designers use because its familiar? i want to know can i break or bend traditional rules of thumb and get a decent result?

They should pretty much work the same at audio frequency if set up according to how the datasheet suggests.

Radio-frequency stuff is weird, and there's way more complexity than a tube datasheet shows.

RF circuit boards have features like curved traces that look pretty wild... there are explanations like signals "reflecting" when they hit a corner in the wire/trace. And you need to worry about the time delay involved with electricity traveling the length of the wire. So when a datasheet says some tube is better for radio frequency than another tube, I would believe it, and not drive yourself crazy wondering exactly why!

Again, this doesn't (necessarily) make it worse for audio use, though you may need to tweak your design (grid stopper resistors, small capacitors in various places) to reduce the presence of RF noise in your circuit, if your circuit can amplify it.

[PRR]

> hi mu dual triodes ...one says primarily used as af resistance coupling amps and another says used as rf or if amps.

What dual triodes are plugged for IF use??

FWIW, the 12AX7 was not an audio tube, it was for Operational Amplifiers.

12AT7 was for VHF RF tuners.

12AU7 is two "general purpose triodes", similar to 6J5. Which is 6C5 improved for better UHF performance. Which is an higher-gain 56/76. Which is a higher gain 37.

6V6 is an improved 6F6, and mostly for audio, though a ton of small transmitters have used these types. At the end when transistors ate the tube share of the audio business, 6V6 hung-on re-rated as a TV vertical sweep tube.

Most tubes are essentially "flat" from DC to 10MHz, limited mainly by the resistances around them. Extreme types in tuned circuits with minimal added resistance do go far past 100MHz, but my geetar don't tune that high.

http://www.mif.pg.gda.pl/homepages/frank/vs.html

[ALBATROS1234]

thank you ...so much gentlemen ! this is kinda how i figured it. im not remotely thinking about starting an amp building company. my imediate goal is to understand how tubes work in an audio fashion, primarily guitar amps, i want to build some for my own use that are exactly what i want out of an amp, i guess the odd tube types appeal to me for a couple reasons. one i want a unique sounding amp, my preference seems to be older valco types going back to the 40s. two i dont have a ton of cash to play with and i have some things on hand to start with. i will list the tubes i have on hand which are from a western electric powered speaker from 1958 a pre 1954 rca radio and the "lot" i purchased recently. when i began reading the tube data i didnt understand why some types that seemed quite similar were designated for this or that.

6SL7gt hi mu twin triode
25L6gt beam power tube
25Z6gt rectifier voltage doubler
12BA6 (qty 2) remote cutoff pentode
12BE6 pentagrid converter
12SQ7 twin diode/hi mu triode
35L6gt beam power tube
35Z5gt half wave rectifier
7F8 med mu twin triode
7F7 (qty 2) hi mu twin triode
7B7 remote cutoff pentode
7A4gt med mu triode
6SJ7gt (qty 3) sharp cutoff pentode
5W4 full wave rectifier
6F6 (qty 2) power pentode
6AH4gt (qty 2) low mu triode
6BX7gt med mu twin triode
JAN 6A8 (qty 2) pentagrid converter

with these i am going to search far and wide and try to adapt existing schematics grafted together and do some playing around with values to get something i hope will be worth listening to. my rough plan to start with the 5w4 rectifier for power, i dont have a transformer yet i think i will do 2 or 3 inputs, perhaps a low,high and mic, the mic may be like an old valco type and have an additional gain stage perhaps using my 7A4gt or a 6SJ7 the other 2 input will have a twin triode maybe a 7F7 feeding plate 1 into grid 2. after that a volume and tone stack followed by another triode to replace the gain loss of the tone stack maybe the 7F8. following that i will try the 2 6F6's in parallel as the output transformer i have is single ended and i seem to like se designs sound. i have a pair of 10" celestions in a crappy ss crate 40watt combo. i figure this should be 4 to 6 watts output and has potential to sound ok. does this plan seem logical?

[ALBATROS1234]

so i was looking on the tube search link you posted PRR and first thing i look up and see is my 7f7 is the same as a 6sl7 except the loctal base instead of octal, i ordered 4 new ceramic loctal sockets. secondly  i looked up the 7a4 and it cross refs to a 6j5. so can i assume if i find a schematic with the 6SL7 in it etc i can use those cap/resist values as  a baseline starting place? i have seen so old valco designs with 6sl7 tubes so i spose i can start there.

[tubeswell]

6SL7gt hi mu twin triode
...
6SJ7gt (qty 3) sharp cutoff pentode
...
6F6 (qty 2) power pentode

You could make a decent push-pull guitar amp using these. I'd try using one (or two) 6SJ7s for the pre-amp gain stage(s)*, the 6SL7 for the phase inverter, and the pair of 6F6s for the push-pull output stage (using a 15 to 25W OT with an 8k to 10k plate-to-plate reflected load, and a PT  (and power supply) that delivers a B+ around 300VDC

*Look for inspiration in one of the Gibson or Epiphone amps that uses small signal pentodes in the pre-amp . (GA20 attached)

[ALBATROS1234]

that looks pretty good tubeswell, i didnt think about gibson amps, i was mostly looking into valco/national types, will check into iy thanks for the input

[ALBATROS1234]

at the moment i have a power transformer that is only hi voltage it puts out 425 with a center tap so its 212 per side. i have a 6volt wall wart for filaments. can i for the time being use my hv diodes for rectification and use my 2 xfrmrs mentioned above to play around with? i know im not the only one ,but i just cant afford to fork over the cash for a new proper multi tap transformer at this time and no time soon. perhaps i can lower the value of the plate resistors to allow more juice to go there. i do have a 5w4 rectifier but no 5 volt xfrmer and i am not sure if the 5w4 could handle much more than one preamp and one power tube and i would like to add more stages. also i only have a small se output xfrmer at the moment so one 6f6 will prob have to do it. i will try to draw a simple schematic later and post it for comment and help spotting flaws if you gents dont mind helping out the handicapped.

[PRR]

As you found, most of the "newer" tube types are the old types in new bottles. 12AX7 is two 6F5 in one.

If you keep buying odd old sockets to suit odd old tubes which may not even be good (!!), you could have bought new "usual" tubes, or even a 2nd hand Valve Jr (an excellent donor).

Different "tone" is more about the circuits than the tubes.

[ALBATROS1234]

thanks prr, that is a very good point, i know i do have much to learn. but i am a quick learner,ambitious and motivated . although i only spent 20 bucks on 16 of those tubes and the 4 loctal sockets were 9 bucks and change shipped.  my main deficiency is a power transformer . maybe an output trannie if the one i have cant handle it. i may need an odd cap or resistor but i plan on making the chassis out of a heavy gauge piece of 2x8 metal stud, i need turret lugs but i have a piece of black fiber board i can cut to shape that i ripped out of an old wall mounted power regulator from the 50s(?) that i got from a building in the french quarter that i am working at right now. my first amp will surely be a hodge podge of parts but i will make it work.

[PRR]

> i need turret lugs but i have a piece of black fiber board

Brass tacks. (Take a magnet when you buy them- steel tacks are everywhere and a thin flash of copper may not solder well.)

Find a slightly smaller drill. Pound the tacks in from the bottom, cut the points off(?), wrap leads on them, solder. Not as self-stay as lugs with holes, but you'll manage.

A saddle-shop may have copper split-rivets, where you can lay wires in the split and solder.

[ALBATROS1234]

thanks thats a great idea, i hope my diy spirit isn,t too cringe worthy. i am trying to make do with what i have and can easily obtain. i thought about using some screws in a similar fashion, why can you not use steel? just curiously, i wont even try if you say don't , you're obviously good at what you do. if i have to guess i would say something to do with soldering disimilar metals. speaking of... i think i read recently that certain tube sockets with certain tubes can cause oxidation, as an electricians apprentice we deal with what they call galvanic corrosion when disimilar metals are connected electrically and we use a product called penetrox mainly when hooking up copper wire to aluminum grounding lugs and such.is that the reason?

by the way merry christmas and/or happy holidays to you and yours thanks for the help.

[PRR]

Steel won't take solder without strong flux which would eventually eat the copper.

I suppose you only need to solder the leads to each other, they can "hang" on a steel nail by mechanical friction/flop.

Penetrox/NoAlOx is for *pressure* connectors, clamps. It tries to keep future dampness out, and the bits of Zinc tend to bite-through the surface oxide on Aluminum (and Copper) for better electrical contact. The Zinc may also be a sacrificial anode? The real problem here is not necessarily "dissimilar metals", but that Aluminum's surface oxidizes instantly, and the oxide is a non-conductor and hard. In small pressure clamps (15A receptacles) it is possible to get enough bite to work when new, but oxide is rust and Prof Young tells us "Rust Never Sleeps". 10-20 years down the road the actual electric contact is microscopic, and any load makes a hot-spot which can lead to fire. We no longer use Al wire on 15-20A circuits and devices: the over-engineered "fixes" cost more than using copper wire. In big work, the connectors are larger, and such work is normally only done by experts. Severe brushing, Al-ointment, and full clamp torque makes big Al connectors reliable.

[ALBATROS1234]

interesting, i actually think i have a hanful of copper nails somewhere perhaps ill try those. know i got brass rod and tube around. i have been building static models of ww1 aircraft for the last 15 years or so as my main hobby, but have been missing guitar and tone so i started playing more again several months back which led me to this tone quest. thanks again for the responses.