supro push pull ot question.

[ALBATROS1234]

i am thinking of building a small supro push/pull with a pair of 6em5 to replace the 6973 type, i know that there are debates on whether the 6em5 and/or 6cz5 are the same as 6973s except pin 1 and 8 internally connected thats not the question i am gonna try it cuz i cant afford $50 for a tube and there is more than one report of guys using these and having jumped the pins on the socket say that these are when compared to 6973s are virtually the same tonally just watch out b+isnt above their limit which is a tad lower ,which i am gonna run around 300 to 315vdc.

the question is i have on hand an operational ot which is sort of a universal type the primary has a common, 500ohm,1000 ohm,1500 ohm and 2000ohm and the secondary has a common and a 4 or 8ohm output. so i would hook up b+ to the 1000ohm(center) and plates of each tube one to the common and one to the 2000 ohm right? its multi-tapped and 1000ohm is the middle point ,i have only done s.e. builds and i think this is right but wanted to confirm. thanks

[shooter]

I looked at a couple data sheets and found this one, page 6 shows plate R @ 250vdc ~~.05MEG

http://tubedata.milbert.com/sheets/049/6/6EM5.pdf

PP typically wants 1/2 that per tube, so if I'm reading correctly, .025Meg is a long way from 1k 

[PRR]

> PP typically wants 1/2 that per tube

For triode mode. Roughly.

With pentodes we normally have a huge "mis-match".

However 2K p-p is suitable only for very "fat" tubes, and really multiples.

[ALBATROS1234]

shooter ok so .025 meg is 25k i need that high of impedance for push pull???

so prr you are saying i may be able to do push pull in triode mode for these tubes at 2k?what do you mean by fat tubes 6l6,kt88,el34?

was my thinking correct at least for hooking this ot up push pull with the center point tap(1000ohm) hooked to b+ and the tubes hooked to the 2k and common terminals?

[PRR]

The CT of 2000r is the 500r tap.

[ALBATROS1234]

I got you because it's impedance not dc resistance. Thanks why I was checking with the pros. I am like a teenager fumbling in the dark trying to find the wet spot. I have been ultimately successful with 4 somewhat original designs but it's been some skill,some luck and some good advice from you guys.

[DummyLoad]

your OT is probably designed as a replacement for 6CS5 or 12L6 types.  6EM5 P-P will want to see a 8K-10K plate to plate load to work efficiently at 300V. lower your B+ to 170-200V to work your OT P-P as you describe with 6EM5.

OOTH, 6CW5 work well with 250V B+ and 3K plate to plate load and make 20W+.

you could use that OT with a 12L6 singe ended and make a lower output (~~2W) champ-like practice amp with 12V fil string and 120V B+. 12L6GT datasheet attached. 12L5 and 6CS5 variants draw 2-3x the heater current of 6V6/6973, so be mindful of that.

--pete


edit: another option - 6GC5 with 170-200V B+ with your OT wired 2K single ended with 8ohm speaker load. makes ~~3.5W.

[ALBATROS1234]

Thanks sir I appreciate the reply. Perhaps I will just buy a more appropriate ot. I had often read 4 to 5k was normal range for ot so I was thinking (likely my main problem) that 2 tubes in push pull might need half that . I do have a pair of nod 6bk5 types maybe I can use this ot  for those. They are about half the output per tube iirc

[DummyLoad]

6bk6 is also a heater current hog - 1.2A; also, 7b5 want's 250V B+ for optimum output and thus higher load Z. spec sheet states 6.5K load. you could use a champ 7K OT with that tube or lower B+ to ~~200V to use 5K Z.

--pete

[shooter]

6EM5 P-P will want to see a 8K-10K plate to plate load to work efficiently at 300V.

You understand that you can up the primary Z by upping the secondary Z (adding more speaker(S))
so if you have 2k @8 ohms, you have 8k @ 32ohms.  AND more speakers looks cooler 

[DummyLoad]

6EM5 P-P will want to see a 8K-10K plate to plate load to work efficiently at 300V.

You understand that you can up the primary Z by upping the secondary Z (adding more speaker(S))
so if you have 2k @8 ohms, you have 8k @ 32ohms.  AND more speakers looks cooler 

no, that concept completely eludes me.     in the meantime, do have a look here - see schema in reply 15.

what you suggest will attenuate LF with 4x load on the secondary - probably well in to the response of the instrument in standard tuning.

try it, it may be just the ticket with 6" or 8" speakers.

--pete

[shooter]

I didn't mean you Pete!  I've been following your dust trail for awhile! and attenuating lows is NOW something i'll add to my toolbox 

[ALBATROS1234]

Good stuff I need to pay more attention to stuff like heater current. Right now I don't have the speakers to do that although the concept of a 4x6 cabinet is oddly interesting. Right  I have 3 8" speakers that 2 are run in series to give me 8 . The third 8" is 8ohm as is the 15". I do have a 5x7 that's out of this 1951 reel to reel it tests 4.5ohm dc resistance it was running a 6v6 and 6k6 in a weird config. I think one was playback and not sure what the 6k6 was doing. Then there's the 4" I got out of a 1950s radio with a 35L6. It's sounding more like new ot for the supro clone and figure out the rest later.i guess I have been lucky and or se is just much simpler cuz everything I built ended up sounding good regardless even if I swap power tube or ot or anything . I am assume it's also partially due to the fact that the most powerful thing I built is 8watts

[shooter]

the most powerful thing I built is 8watts

If you get 8w sounding good to you, 80w is just scaling up 

experimenting is probably my best engineering tool 

[ALBATROS1234]

My point was not so much power but the fact that lower wattage amps are usually pretty simple. Every amp I have built has been ss rectifier and 2 tubes single ended with a pre and post volumes and a tweed style tone. Higher wattage amps have tubes total for one .usually phase inverter and a tone stack, reverb and/or tremolo. 2 to 4 power tubes. It seems as though all these bells and whistles would contribute to a much larger balancing act.

[sluckey]

Step out of the box. Come to the dark side. Bring money.

[shooter]

Step out of the box. Come to the dark side. Bring money.

NICE, need to put that on my business card 

I'm an outlier here, I like simple, 2 knobs work fine, most guitars have enough already, and if not, they have pedals.  I agree the PI adds complexity, I solved that by stealing from the '50s and went with a tranny, still not free, but easy, and liked.  You can REALLY annoy the neighbors with 1 PA tube and GOOD speakers.  Do it like Mr. Cash, 1 piece at a time   

[ALBATROS1234]

so youre saying if i get one piece at a time i came have a 51,52,53,54,...67 supro. lol . love that johnny cash song.

on another note thats kinda what i am doing, trying to nab a bit here a tube there, and old chassis with a transformer here or there, and yes it is addictive and i am already wandering the further in the dark looking to ressurect the bones of tone.i dont now what it is but i just love the tone of that old valco stuff, i may build a spectator clone first( got 1951 national union 6sl7 and 6v6) i got a couple 12ax7 projects i want to do one of which is the supro 1624t above mentioned with the 6em5s subbing for 6973s. i got a 6bq5 begging to be in something may do a pentode preamp with that as well as this sweet 5881 and a humongous 6l6g that  have to get a new pad. so i got my work cut out for me.

i know it may be blasphemy here but i find that many things that people say not to do seem to work like i have tube rolled in my last thingy with power tubes stretching from 6f6,6k6,6v6,5881,6l6g and all sound good, some sound better but if i look at the rca book they all should have different kathode resistors etc.etc but they all work fine through the same se ot that i got out of an old western electric powered speaker using a 25L6 for power. no clue what the impedance even is just hooked it up, nothing really gets hot(slightly lukewarm power transformer) but that doesnt seem out of order. in a way i hope i blow some shit up so that i learn the actual boundries rather than the spec suggestions.

[shooter]

i hope i blow some shit up

It might be fun ONCE, but a quad set and OT, might set you back REAL money.  There is pretty easy math that keeps you from stepping over the edge.  I like doing what you are, one of the fun things for me is run #'s checks, measuring gain, max plate, etc.

keep feeding the addiction, rehab is for wimps 

[ALBATROS1234]

lol , i am just having fun learning and trying to experiment to create different tonal textures. and i appreciate the help you guys are giving me as well as other points of view on other concepts of amp building.