frankenstein - frankenamp

[DummyLoad]

aka metal-mania. que up edgar winter's frankenstein. if rosie the riveter rocked, she would've built an amp with these tubes.
yes, you can see some fender 5E5 in it... a lot actually. slow day at work... doodling again.
 
 
all valves metal envelope.
hy-gain.
~30WRMS output.
1614 output tubes - metal version of 807 w/o plate cap (errr...).
deluxe like.
matchless like - red-headed pentode out front.
modern(?) schmitt splitter.
dual 5Z4 or 5T4 recto - less sag.
modern iron.
low hum - modern DC supply to filaments for pre-amp valves.
built (to be?) using vector brand octal turret sockets.

thoughts?

--ISO
 
edit - correct schematic attached

[stingray_65]

Iso

I hadnt seen this post till now, looks interesting!

I've seen a lot of your "doodles" have a pentode in the preamp section, I'm guessing it's a "sound" that you like.

I've only done 1 build with a pentode in front of the power section (Gezzer and Tubenits TOS) and boy it sure does overdrive!

Are you getting the same effect here or in your other "doodles"?

or is it not an overdive?

enlighten me a bit !

Ray

[DummyLoad]

actually the pentode side is "cleaner" overall, and yes, i do like the sound of a pentode. i also like the sound of raw triode distortion. in this case (and my other posts) the cascaded triodes have more gain overall than the pentode does. with the pentode you can crank up volume  and use the guitars volume to go from clean to overdrive. it is difficult to describe tone, so i won't even try. if i want triode (BF dlx) tone i turn down the pentode vol. if i want only pentode (a-la matchless) then vice-versa. mix the two and you get some wild stuff depending on the levels of each channel along with some interesting tones from cancellation. give breadboarding a try or find a scrap chassis to "doodle" with and see how you like things to go together.

lastly, channel switching to me is PITA and can get overly complex in a hurry, easily becomes a source point for parasitic osc., and did i mention it can be a PITA?     

IIRC you have a CNC, right? roll your own BB. i can email you the plans to ours in DXF format, or follow link below to other good ideas.

http://www.tubelab.com/The_Tubelab.htm

HTH & respectfully,

--ISO

[Tone Junkie]

ISOTone I love your designs you really think outside the box using all these unusual tubes there probably the best ones out there its just us regular Joe,s dont have much knowledge of them. Keep up the good work and give us clips when your done . Bill

[DummyLoad]

TJ, much thanks. <blush>

i just look for other alternatives for valves. i seems as though the commonly used NOS stuff is just too unpredictable nowadays - as in were down to bottom of the barrel - so to speak, while the russian and chinese stuff are plagued quality control roller-coasters.
take for instance the metal clad tubes in this proposed potential calamity, i'm thinking that with some silicone rubber damper rings, they'll be no more or less microphonic than any current production or NOS valves available and sound just as good.

there are plenty of other NOS valves out there that will do the job we ask of them, aren't necessarily the last of the pickings and if you can live with not being able to hit up banjo center for instant gratification replacements, then you can build some cool amps with them. just stock up on what you'll need to last a few decades. don't build something you're going to gig with with frequently. if you do, then plan on hauling along a tube caddy full of spares.

i spend many hours sifting through data sheets in my spare time. reads: ISO doesn't have much of a life...   

you don't want to hear my playing - trust me. i have a friend who is a decent musician lined up to record some clips, but getting him to follow through...   

happy rosin smoking...   

--ISO

[Jack_Hester]

i spend many hours sifting through data sheets in my spare time. reads: ISO doesn't have much of a life...

I enjoyed your schematics and doodles.  I've spent the past year trying to 'learn back' what I used to know.  And to give credit where due, I've enjoyed this entire forum.  The one thing that I've noticed about your schematics is the detail.  That's what annoys my wife about me, when it comes to drawing.  She says that I spend hours just staring, and only minutes at actual drawing.  It's actually only a couple of hours at a time.  But, I'm thinking that she may be speaking in dog hours.  Anyway, keep doing what you're doing.  Gives me more to stare at and possibly a use for all the non-standard tubes that I have.  Fine business.

Jack

[DummyLoad]

jack, thank you. i'll keep on posting "odd-ball" things for you guys to mull over.

  

[DummyLoad]

having a blast with the proto-board again. after dismantling the unnerving glo-champ, i built this amp on the board. it's much more fun to play. with more gain and just hint of sag with recovery nearly immediate. playing through a eminence red-coat 12" in an open back enclosure. 

i made two versions. having never fooled with metal cased power tubes, the first version used 6L6GC b/c i'm a puss. all went well, however, the tweaks on V1 were not getting things done as i'd hoped, and the triode path (V2-3) was braking up much too early.

in version 2 i returned to standard 100K Ra for V2 and made some changes to V1s bias as well. at that time i decided to fire up the metal cased tubes. all went well, but i did have to swap out 2 tubes before i finally got a reasonably close matched pair.

man them tubes stink! (le-pew! le-pew!) the paint cooking on those things make for some funky smell when they get toasty. tubes are idling @ 12W ea. (roughly 400V to plates @ 30mA Ik) and they stunk bad for about 2 hours. i don't know if my olfactory just became acclimated, or if it just cooked off the stench - maybe some of both?

schematics of both prototypes attached. both have telemetry recorded. the .sch has 2 sheets - ver.1 and ver.2

enjoy!

--ISO


  

[stingray_65]

I keep getting drawn back to this amp you're building,

You say it's 5E5 inspired, and I can see that in the tube count, but when I get to your PI I get lost.

I love the topology of the preamp ALOT! and it makes me want to experiment a bit.

But the last time I did experiment it was with a 5E5 and I added an AC30 Top Boost to one channel and it was AWFUL! fun experiment, big dent to the wallet!

I've still got the Iron and had salvaged a few other parts  so all is not lost!

It's great to see how you work around you're arbitrary limits. IE all metal tubes, BK's, all octal,all loctal etc.

I'm really interested to see where this all ends and where it might go, and i'm really curious as to how this amp might sound with more "traditional" audio tubes.

I might just have to build a little prototyping station just to see!

Ray

[DummyLoad]

You say it's 5E5 inspired, and I can see that in the tube count, but when I get to your PI I get lost.

please forgive, i should have elaborated further. the tube count is irrelevant. the preamp is a 5E3 + the matchless DC30 pentode replacing the second input triode. both 5E3 and pentode inputs are bonded to same input jack. the PI is 5F6A like. the output stage is 5E5 inspired, only with an OT with less primary impedance with higher power and current ratings. it's what i had laying around - the PT i found on a diy classifieds unused for about 1/2 of retail including shipping, so i bought it. the choke is a left over from the glo-champ experiment.

i was thinking about a reconfiguration - convert 1 of the LTPI 6SF5 to 6SC7 and use that as LTPI then use the leftover 6SF5 for a driver stage for the pentode path -or- perhaps replace it with a low mu metal clad tube like the 6R7.

 

--ISO   

[DummyLoad]

hmmm...

have a dilemma. i installed a pair of NOS 5881s, GE branded. they came up OK filaments were glowing normally, idle current draw was within reason (24mA and 29mA), however, after warm-up and i started to play the amp it was distorting grossly. i noticed also that the filaments were dimming with current demand, as i played the filament on one tube espcially would almost extinguish. the other dimmed only slightly. the gettering looks ok, except there is a very narrow <1/16" light gray ring around the edges. i presume these tubes are gassed and should be tossed?

thanks

--ISO 

[darryl]

Do you have another amplifier available which could be used to try the 5881's? If the problem follows the valves, at least one of them is faulty. If they work OK in the second amp, the problem is in the original amp.

[RicharD]

hmmm...

have a dilemma. i installed a pair of NOS 5881s, GE branded. they came up OK filaments were glowing normally, idle current draw was within reason (24mA and 29mA), however, after warm-up and i started to play the amp it was distorting grossly. i noticed also that the filaments were dimming with current demand, as i played the filament on one tube espcially would almost extinguish. the other dimmed only slightly. the gettering looks ok, except there is a very narrow <1/16" light gray ring around the edges. i presume these tubes are gassed and should be tossed?

thanks

--ISO 

Sounds like Molexia to me.  Check them bread-board connections or swap for a known set of tubes.

[DummyLoad]

Sounds like Molexia to me.

no, i do not believe this to be the case - pair of 6L6GC and pair 1614 work properly in same sockets. 

[DummyLoad]

Do you have another amplifier available which could be used to try the 5881's? If the problem follows the valves, at least one of them is faulty. If they work OK in the second amp, the problem is in the original amp.

swapping the tubes in the same amp the problem follows the tube - they are likely gassed - have never seen it that bad thought - not to the point of filament nearly extinguishing.

sadness...i have eight of them. all GE made in canada tubes bought as one lot - they all do the same thing to varying degrees. it seems that i bought junk, but then again i'm happy - buttery finally made it over and hung out for a while. he seemed to enjoy playing this amp a lot. we sampled RCA metal outputs, black plate RCA, and glossy black plate GEs - i believe that the final consensus was that the RCA black plates were the smoothest.

 

[DummyLoad]

ok now, after diddling with the pentode path until blue in the face, we decided to scrap it.

the triode channel sounds so good with the 6SC7 LTPI, we pulled the 6SJ7 from the plan completely.

if you build this, you won't be disappointed. build it with plenty of space - it does hy-gain exceptionally well.

no NFB necessary. add it if you wish - use the fender bassman 5F6-A plan.

3 little metal cans & 4 big metal cans - no string needed.  



EDIT: fixed schematic - filament chain.

[Tone Junkie]

Looks like a very neat project my friend some day I want to do a metal amp too. All pun intended I like the idea of all metal valves I bet it looks killer. Bill