Glo Champ

[DummyLoad]

inspired by PRR. a comment he made about using a HK257B/JAN-4E27 a while ago in a thread long buried. just fooling around with sim, i was pleasantly surprised to see hammond winds all the inductors one would need in the configuration presented.

hopefully he'll chime in and set me straight - could possibly consider building, but the iron alone will be well over 300$. for now it's just an exercise.

i call it the glo champ because PRR mentioned that the HK257B glows in normal operation...  :glasses9:

http://tubedata.milbert.com/sheets/114/h/HK257B.pdf

yes, i know it has a LOT of gain... possibly totally unusable - like an 800HP street car.


--ISO

 

[eleventeen]

Holy crap! I probably gave it away but I had a NOS 4E27 I would have glady contributed to the effort.

[PRR]

Nice set of iron.

I get an iron-cost of $321 plus SHIPPING. (Did you add-up the weights?)

There's no way it needs 1,000uFd filter caps. It should work with a "Champ" filter, except scaled 1:3 to account for the 3 times lower stage impedance (2.5K versus 7K). The choke is not essential but for $30 ya may as well. You could probably go 50uFd per section (two 100uFd to stand the voltage) and be dead-clean.

C5 may need to be a bit more than 2uFd if the main supply is just-good-enuff for the plate/screen. Or maybe not: the 39K adds a lot.

It's a hot expensive tube working dead-Class-A. Let's SELF-bias it for added safety. It's only about 6 Watts more heat in the chassis. 36V/160mA is a bit over 220 ohms at 10 Watts.

Two power switches: one for the big filament and one for B+. The data does not say the filament requires pre-heating, and the B+ is not terribly high (28% of rating!), but we are just enough above "receiving tubes" that it would be a good idea.

My inclination would be a two-triode preamp and driver. Keep the first prototype mellow and stable. Jazz it up later.

This may be a "hard" tube, high output impedance. Low loudspeaker damping. Guitar speakers work with low damping, but you may want a hint of NFB. Depending on speaker and desired tone.

The power grid coupling cap scales with the grid resistor. Big tubes want smaller resistors. I don't see a Max Rg1 for this tube. 100K is certainly the most I would try. For small geetar amps we would use 0.01 or 0.02 into 220K-470K. This is a big amp (and big OT!) so we may like more bass. 0.05uFd can be a trial value.
EDIT: http://www.mif.pg.gda.pl/homepages/frank/sheets/088/4/4E27A.pdf page 2 shows 250K max. We can use standard Champy values.

Two 1N4007 are OK for voltage but kinda close to peak current rating here. That's a bad place for a shorted diode. Look for the 2A series.

[mresistor]

What level of power out are you looking to get from this puppy?  
100watts? 75 watts? 150 watts?

[DummyLoad]

What level of power out are you looking to get from this puppy?  
100watts? 75 watts? 150 watts?

it's a paltry 25W.

[DummyLoad]

(Did you add-up the weights?)

i think i got a hernia from just adding it up. 

C5 may need to be a bit more than 2uFd

duly noted... sim showed 5t at around 1.5 secs w/ 2.2uF... had to revamp nodes B and C with 4 triodes - 10uF shows 5t around 1.5 secs w/ 27k - should be good enough for champ work?

Let's SELF-bias it for added safety.

done!   

Keep the first prototype mellow and stable.

compromise - 4 triodes... 1st stg. av is ~45 second ~48. fiddling with sim and 6SL7 - can't seem to get anywhere i like the input threshold with a single SL7 tridode - 2 || triodes seem better on paper/monitor, however, that can change. why am i sticking with the 6SL7 then? i have box full of them... 

Two 1N4007 are OK

thanks, duly noted. i need to pay more attention to the pk ripple currents when "throwing" a power supply together.

another thing i noticed on sim is that the grid stoppers for the 6SL7 seem small... must be the miller capacitance w/ || triodes - i assume that with 2 triodes in || the miller capacitance doubles. HF -3dB roll-off is ~40kHz. w/ 15k grid stopper.

i found a source for the 4E27 in NOS and i have funding for the iron. the socket for the 4E27 seems a bit difficult to locate as is the plate cap.

attached a revised schematic.

PRR, thank you for your time, it is immensely appreciated.

--ISO



 
 

[PRR]

NFB won't work with that cap there.

You say 4 triodes but I see 2? Oh, parallel.

> grid stoppers for the 6SL7 seem small...

You may not need stoppers on the 2nd stage (the first needs something to knock down AM/CB radio). If you do need them, you may need separate stopper for EACH grid to stop (unlikely) push-pull oscillation between the two halves.

The HF -3dB is probably dominated by the 500K pot, and is quite fine.

> can't seem to get anywhere i like the input threshold

It would work fine with 20mV input for full output. We need 36V peak or 26Vrms at the power grid. We need 26V/20mV= gain of 1,300. We can't get that in one stage. We can get that in two stages of gain=36.

What is gain of 6SL7? GE data says the first stage (as one section) with 510K load can give gain of 46-48 with Rp at 240K or 510K. If you must parallel, use the Rs=1.0Meg line, gain of 50. For the second stage with 240K load one section gives gain of 37-42 and with 300V supply over 40Vrms at 5%THD.

So using Rp optimized for the effective load, instead of an arbitrary(?) 68K, you can get gain of 37*46 or 1,700. 26V/1700= 15mV input sensitivity.

The power tube and OT need 26V in for 14V in 8 ohms, gain is 0.54. The driver stage has gain of 37. The open-loop gain is 37*0.54 or 20. For guitar, we probably do not want much NFB in nominal 8 ohm load, We want to control the 10X rise of gain at the speaker bass resonance. So we pick a NFB ratio higher than 20 but less than 200.

If you inject NFB at the handy ~~1K driver cathode resistor, that resistor is unbypassed and that stage's gain is lower, perhaps half. We can't afford that loss of gain. Look at the last, AA Champ: NFB is brought to a 47 ohm resistor under the bypassed cathode R-C network. The 47 ohms does not hurt gain enuff to matter. Then the from-OT resistor may be over 940 but under 9K4. 2K, 3K, 4K, whatever is handy. Adjust while tweaking the speaker driver and cabinet selection.

I ran some sim and the 1N4007 does have enough current rating; you do of course want to double-up for voltage.

It may be the same socket as the 813? 813 was very common.

U7G
Giant 7-Contact

http://thetubestore.com/7pinbig2.html

If you keep the kids out, the plate contact could be a Fahnestock clip. This also pulls heat out of the seal.

[DummyLoad]

...instead of an arbitrary(?) 68K,

datasheets - rp=44k  assumption: 2 triodes in || rp= ~22k? Ra ~2x rp = 44k. sim liked 68k - symmetrical output and decent av.

re-ran sim with a close to your suggested Ra value of 220k, with one triode - results are:

1st stage - bypassed
Vb = 330V
Ib = .95mA,
av = 55
Rk = 1k,
Vbias = ~ -1V    

2nd stage - not bypassed
Vb = 380V
Ib = 1mA
av 33
Rk = 1K8
Vbias = ~-1.7V

ok, so back to one not so little bottle.... one ginormous bottle...  

ok, so now we have one not-so-little bottle drawing 300mA of heater connected to 5A winding... that should be interesting - wanna bet we'll need a series shunt to tame the heater supply? - and yet more heat... ugh!

if it were to be, it would be built with a cage over the 4E27 - unequivocally.

revised schematic attached.

--ISO


EDIT: did not change NFB  R values in schema... shame on me!

[DummyLoad]

one step closer... digging though my parts, i found a NOS stancore P-6165 power transformer - ratings: 800VCT @ 200mA 5V @ 4A; 6.3V @ 5.5A.

problem is, with stancore and SS recto, B+ at node A is about 560V on sim. - don't know how delicate the g2 is on 4E27 - uncharted territory, however, with two 5V4GA the B+ sims at about 490V and we'd have to drop capacitance and live with some buzz. or, we could stick with SS recto and let 4E27 plate have 560V; burn off ~50V with another RC stage in the PS chain for g2 and keep stiff filtering. decisions, decisions...

 

[PRR]

Bypass V1b cathode resistor.

I'd smoke-test with more than 100 ohms in G2. 1K at least. You may have to reduce this for maximum Watts, but something large will make it more robust against shakedown-cruise accidents.

You should get a sub-miniature twin-triode to drive the big bottle. {G}

Anybody but you, I'd be nagging about exposed 500V. Obviously a no-kids no-pets workshop.

> wanna bet we'll need a series shunt to tame the heater supply?

No, put 1 or 2 ohms in series with the little heater. Not urgently.... the tube will live years at 7V.

Big tube cathode resistor wants to be bypassed or you'll need a LOT more drive.

> B+ at node A is about 560V on sim

Minus 36V self-bias. Minus 25V-50V loss in OT primary DCR. You are near 500V, G2 is rated 750V.

At idle, screen at 500V, suggestion says 10mA G2 current. This is 5 Watts, G2 is rated for 25W.

With plate swing, G2 current hits 60mA, 10mA, <1mA. I don't think the average G2 current will be over 15mA-20mA; maybe 30mA in sustained gross clipping. That's 15 Watts, meanwhile plate dissipation is fallen from 75W to maybe 20W, the screen is not being cooked by the plate.

I think it is well within ratings except right AT the cathode current allowed. And you are unlikely to need the hours or reliability of a broadcaster or a radar system. I do think self-bias is warranted just to steady the cathode current; otherwise I think it is plenty within-ratings for your uses.

http://www.classiccmp.org/rtellason/tubedata/4E27.pdf
50 bux: http://www.tubedepot.com/nos-4e27.html

[RicharD]

>Anybody but you, I'd be nagging about exposed 500V. Obviously a no-kids no-pets workshop.

With a crazy master electrician looking over his shoulder.  This should be a 2 person start up.  I have some 25kV URD (neon) wire around here someplace. 

[DummyLoad]

You should get a sub-miniature twin-triode to drive the big bottle. {G}

 

is there a sub-mini TT that can stand enough B+ to drive it? closest thing i can find that might do the job are 6112 or 6948. i'm diggin' sub-mini driver approach - David vs. Goliath.

sim likes 6112A even with 330V and 380V. both 6112A and 6948 are available for not-a-lot of cash.
they are guided missile tubes.  :glasses9:

6612A - 1st stg.
Vb = 330V
av = 52
Ib = 900uA
Vb = -1.61
Rk = 1K8
Ck = 22uF
Ra = 220K
RL = 1M
Vo max = ~80Vpk

2nd stg.
Vb = 380V
av = 52
Ib = 880uA
Vb = -2.4V
Rk = 2K7
Ck = 22uF
Ra = 220K
RL =220K
Vo max = ~105Vpk

how about just combining PS node for 1st & 2nd stg. & dump last RC net in PS and run both stages @ ~380V?


i'd smoke-test with more than 100 ohms in G2. 1K

ok, will do.


this is gonna be fun... fail or succeed.

buttery is licking his chops - we'll be bread-boarding something almost as weird as he is...  

updated schema attached.

--ISO


EDIT: almost forgot... with lower sec. DCR of stancore PT, Ipk is ~1.25A - we'll prolly need to use 2A diodes.


 

[DummyLoad]

50 bux: http://www.tubedepot.com/nos-4e27.html

out of stock... rolled the dice on fleabay...   

OT, Fil, and choke on the way... found three of the 6948 sub-mini TT they are also en-route. 

[PRR]

> dice on fleabay... 

I see there's several genuine Heintz & Kaufmans, and demand is slow.

> found three of the 6948

Don't use them above 80,000 feet! (Where are you, about 1% of that height?)

The big datasheet only has amplifier tables to 250V. I think they were being very conservative (can't change tubes halfway to Moscow). The 250V condition just *barely* drives the HK257B at 5% THD. IMHO the Champ's driver should run light, take strain in the 6V6 and maybe 1st stage. So I agree with going ~~400V driver supply for stage-use. 380V on 1st stage "may" be "too clean"; ya might leave a stray lug so you can drop it to 250V so that a heavy pick-arm will warp the 1st stage a bit.

So you are committed. Either a 30W 50lb amp or 40lbs of trunk-ballast for the next time it snows.

[DummyLoad]

about 1% of that height?

give or take...

380V on 1st stage "may" be "too clean"; ya might leave a stray lug so you can drop it to 250V

gotcha!

Either a 30W 50lb amp or 40lbs of trunk pick-up-ballast for the next time it snows.

[DummyLoad]

slow but sure.... 5VCT 10A filament xformer and 8pin sub-mini socket are last items on hit list. hoping they should arrive before weekend.

had a minor health set-back last week, a cardio pulmonary infarction got the best of me for a short while. getting better and eager to ramp up this project to fruition.

--ISO

a "small" collection of parts for a such a simple amp... 

[RicharD]

>cardio pulmonary infarction

Big words that mean, "scare the piss outta your friends and family."

Land of hard knocks around here.  I'm nursing a sprained possibly broken wrist.  Typing 1 handed is a drag.

[DummyLoad]

drag dude...  :( hope it heals quick - one question tho... hole hawg? 

[DummyLoad]

almost there...

wired and ready for power - it's late and i'm going to wait until tomorrow morning so i don't melt myself down with an oopsie...

[RicharD]

Call me.  I wanna be there for the fun.

[simonallaway]

This looks very cool 

I'm wondering why the plate terminal is on the top of the tube...as implied earlier that seems incredibly dangerous. Does it help with cooling somehow?

[PRR]

1) The original 6L6 is limited to 360 volts because the _base_ was not good for higher voltage.

While there are some Plate-on-Base Octals with 800V ratings, and there are bigger bases, BIG tubes need HIGH voltage and usually put the plate not-on-base.

Nearly all TV H-sweep tubes were top-cap. The average voltage might be 300V, but the peaks were several thousand volts.

2) When you work a tube millions of times a second, the current-flow drags on the insulators and causes heat. Taking the plate out the top in a simple seal is less drag than through a bottom seal, base, pin.

3) Amplifiers tuned for very high frequency operation are prone to internal positive feedback from output to input. Keeping the output (plate) away from the inputs (grid and cathode) allows higher gain at higher frequency.

4) Radio power amplifiers usually have totally exposed plate-coils. That little plate-cap is the least of the lethality. IAC, the power-amp signal is too crappy to let out in public, must be filtered, so the amp itself must be metal-sealed.

807 is 6L6 with top-cap for higher voltage and higher frequency.

What ISO is doing, none of this really applies. But what he's doing is just too unusual to justify a special tube-type for low-volt low-freq uses. He "should" get his 25W with a pair of 6L6; cheaper and lighter. I don't know who encouraged him in this folly .......   

[andrew_k]

I've been away from forums for a few months, but I'm so very glad I found my way back here. Good luck lighting up this wonderful contraption.

[Willabe]

PRR wrote "I dont know who encouraged him in this folly"

Yes,  hummm...... ???       I wonder who..... ???               


      Brad               

[DummyLoad]

He "should" get his 25W with a pair of 6L6; cheaper and lighter.

ugh! and join the masses that have already done as such? we're going where no champ has gone before.    

buttery made it over... he's playing the glo champ as i type and post... he did stop playing for a minute...

he: something's smells like it's burning...

me: is it on fire?

he: no...

me: then keep playing, it's just the plastic on the sacrificial test lead plate cap

he: oh... OK.











 

[Willabe]

ISOTone,

Man, when you said "GLO Champ" you were'nt kidding!  WOW! I bet that thing is brighter than Rudolphs red noise.  :glasses9:  Dont forget your eye protection.        

Now that is cool. How about maybe a pic with the lights off? I bet it looks even better in the dark.  Man, you are one "Mad Tube Scientist"     :evil1:    Very cool!

Hows it sound?


     Thanks,    Brad

[DummyLoad]

Hows it sound?

like a really loud champ and really nice. it needs a 6j7 front end though to take it into heavier feedback. that's in the works.... <evilgrin>  

btw, PRR, there is no NFB and we left the Rg2 @ 1K. it just sounds so good where it is we didn't mess with it. it fired up on the first go - no mistakes - i triple checked wiring over of a couple of days.

buttery made a comment right after firing it up... "i hate to say it, but you're red-plating!" i replied: "why do you think it's called a glo champ?"

 you said it would red-plate... it does.

Dont forget your eye protection.  

and ear.  

How about maybe a pic with the lights off?

good idea! i'll take one tomorrow.  

[Willabe]

ISOTone,

It sounds great too,     

Looking forward to lights out pic.

Are you thinking of making your cab so you can see the "Glo Tube". Maybe some of that metal open lattice type they use on house radator covers for the a see through front?

ISO, you cant hide that thing, he he,"Gotta Let that thang Shine".     :sunny:    :glasses9:   

   
     Brad


     

[RicharD]

It does in fact sound very much like a Champ, but with a LOT more body.  Great dynamic control from clean to mostly dirty, it doesn't go over the top... just like a Champ.   It's very special.  the sub-miniature tube is the icing on the cake.

Obviously this thang is dangerous in more ways than one.  I measured > 400 degrees Fahrenheit + > 500VDC on the plate  = yeah baby!  This should definitely be a 1 of a kind build.  The tubes need to show but be inside of a cage, a sturdy cage, large enough to allow heat to dissipate, and installed with tamper resistant screws.  For use by authorized personnel only.



 :icon_thumleft:  Esoteric build of the year.  :icon_thumright:

[DummyLoad]

it doesn't go over the top...

and now it does... self forgot to install Rk bypass on big bottle. i was wailing it @ 7:30 this morning. with my $#!tty geetar playing, the neighbors just gotta love me.

   

EDIT: almost forgot, i found a suitable sub-miniature pentode for audio as alternate 1st stage... it's the 6788. i could find only one specimen for sale in the wide world or URLs, of all places, on ebay... go figure... it's on the way.

 

[spacelabstudio]

We need to hear a recording!  Surely someone in Austin TX has a decent microphone and mic preamp they can bring over.

Chris

[simonallaway]

This could be the solution Al Gore has been looking for....that amount of heat could run a Stirling Engine 

[tubeswell]

Impressive. Soundbyte?

[PRR]

> forgot to install Rk bypass

D'oh, missed that. (Or thought it could wait until after smoke-out.) The driver will overload just after the big jug overloads; the final stage won't go into heavy clipping. With Ck, it should go 6dB past clipping, a good balance.

I'm uncomfortable about the plate lead. Not the clip, but the cheap PVC wire draped over unknown terminal screws. I have seen similar construction arc out of PVC when heavy signals and plate-swings happen. Do youse guys know an electrician with some THHN wire scraps? Or a hot-rodder with solid-core spark wire? Or the small nylon tubing used for ice-maker water feeds.

How's the hum?

[PRR]

> I measured > 400 degrees Fahrenheit

That's not hot. 6550 at 560V 40Wpd will hit 414 deg F.

Play LOUD. Plate temperature will drop. (Since it glows, you may see it.)

Since it is not hotter than some tubes routinely run nearly open to the world, the main safety issue is the exposed 500V. I have thought about a "bridge" over the tube, hiding the plate connection, holding it into socket, with columns down to chassis with disconnects so that when you remove the bridge there is no voltage above chassis. More mechanical work than I can do.

At that temperature, hardwood will last a very long time. It'll blacken where it contacts the glass, but won't burn, at least not for decades.

The plate pin will need cooling at or above the power you are at now, to keep seal temperature down. If touch-proofed, a fahnestock clip might be suitable and appropriate.

What is the tube? If 4E27, Eimac calls it 200mA 125Wpd. You can't even get there. The 4E27 can often replace HK257 in class C radio work; it is a lesser choice for A1 audio at 500V because you will only get ~~280mA peak. Therfore your 145mA cathode current is about spot-on for symmetric swing. 4E27 does not turn-on as easy as HK257; if you did want to try higher current for better match to 2.5K(?) load you'd need less than 220 ohms bias. One thing and another, I think you hit on a best-bias condition first try.

> Soundbyte?

Should sound like a Champ through a little PC speaker. If speakers are good, you might hear that this OT has more  bottom octave than the average Champ OT; but you could build a 7W Champ with proportionally equal ballz.

Only way to get a "size" reference would be to A/B against some known amp like a 5F6A. (Yes, I suspect it won't be overwhelmed by a 5F6A.... less body more soul.)

[DummyLoad]

> forgot to install Rk bypass

D'oh, missed that. (Or thought it could wait until after smoke-out.) The driver will overload just after the big jug overloads; the final stage won't go into heavy clipping. With Ck, it should go 6dB past clipping, a good balance.

I'm uncomfortable about the plate lead. Not the clip, but the cheap PVC wire draped over unknown terminal screws. I have seen similar construction arc out of PVC when heavy signals and plate-swings happen. Do youse guys know an electrician with some THHN wire scraps? Or a hot-rodder with solid-core spark wire? Or the small nylon tubing used for ice-maker water feeds.

How's the hum?

it's called poly-flo; used to use in oil-patch for FID gas chromatograph, total hydrocarbons, and H₂S detectors... i can get some from HW store... the test lead i'm using has 2mm jacket over 24ga wire. i have some THHN but it's solid conductor and it's springy to form; i'm afraid the alligator clip will pop off. buttery said he had some neon lighting wire, i'll horse-trade  a small piece off him. i don't have any fahnestock clips, but definitely need to come up with a permanent solution. these look like they'd do the trick... but no insulator. i'm sure there was a plate cap made for these tubes, i just can't seem to track one down, and that's really what i'd like to have.  

the hum is there, not as bad as i thought it would be, but hoped it would be better. i think it'll clear out a bit more in a permanent home + the wiring of that sub-miniature was tricky - i had to use 24AWG to keep from shorting to the adjacent pins as i don't have anything smaller - i just couldn't track down any wire-wrap wire. i imagine some of the hum is contributed by the 5VAC directly heated K of the big bottle.

i did run the thing up to 120VAC on the line with a final of 550V to plate of 4E27A with right at 150mA for Ik. i must admit i was a bit nervous taking it beyond 140-145mA, however, i did play it for an extended period of time this evening and it seems happy. the telemetry in the photo's i shot last night were with 115VAC on the line.

i'd like to tweak Rg2 of the 4E27A and see if we can squeeze a bit more out of it, Rg2 is @ 1KΩ now - do you think it would be a reasonable progression to 500 and then possibly as low as 220Ω? more to the point, if the g2 diss. is limited to 25W would 10-12 watts at idle be an acceptable target as long as Ik does not exceed 160mA at idle?    

lastly, much thanks again for the guidance. it is comforting to have expert eyes looking over your shoulder...

respectfully,

--ISOTone

[DummyLoad]

Are you thinking of making your cab so you can see the "Glo Tube". Maybe some of that metal open lattice type they use on house radator covers for the a see through front?


absolutely!   

[VMS]

Hi ISO.

Have you seen this page:

http://www2u.biglobe.ne.jp/~tossie/FJ-4E27-J.html

There is a picture that shows one way of doing the plate wire.

Also, there is some type of humdinger on the heaters.

[Willabe]

       What is that Russin?        :confused2:

Would be interesting to read the projects text.  Oh well.     



    Thanks,    Brad

[RicharD]

I do have some neon URD wire rated at 15kV.  I also have some asbestos jacket wire rated for 1000 degrees Fahrenheit.  I think that's #12 though.  the URD is a lot more insulation than wire but I'm certain it's PVC.

I like the idea of a kill switch associated with the cage removal.  I can think of 2 ways.  1 being a receptacle mounted to the chassis whit a jumper plug mounted to the cage.  the other being a limit switch activated by a pin attached to the cage.  If you do the limit switch, it could be a SPDT with the open side connected to a fast drain resistor.

[DummyLoad]

      What is that Russin?        :confused2:

Would be interesting to read the projects text.  Oh well.    



    Thanks,    Brad

japanese - i love his power supply - the 5R4 and the C-LC-LC stages... imma have to sim that - looks likes it'd be pretty quiet. i've got a potato masher 5R4GY & some 200 mA hammond chokes collecting dust.

 

[DummyLoad]

What is the tube? If 4E27, Eimac calls it 200mA 125Wpd

it is the EIMAC 4E27A. interesting to note that the EIMAC has a .125in. (1/8") plate connector and the HK257B has a .068in. (~1/16") plate connector. i'll order up a bag of the fahnestock clips tomorrow.

i'll decide what to do about the cage once i have a better idea about the mechanical layout, but what i was thinking was the transformer plate wire is attached to a contact that sets in a G-10 fiberboard nacelle in the base. the plate wire itself is attached to a contact in end of a G-10 fiberboard piston that is attached inside the cage and spring loaded. it disconnects from the nacelle when you pull the cage off. think of it as a large momentary push-button switch - only the plunger comes apart.

[PRR]

> a 0.125in. (1/8") plate connector

Octal pins are, what? About 0.093"? Can they be made to stretch 35%? 

I'll be darned. EBY is still in business. http://www.ebycompany.com/

> a picture that shows one way of doing the plate wire.

The relevant part extracted (attachment below). Japanese (especially technical Japanese which uses old and borrowed words in new ways) can't so much be translated as understood and reconstructed in another culture.... which machine translation can't do. However "naked is inconvenient" comes through rather well.

[PRR]

> tweak Rg2 of the 4E27A and see if we can squeeze a bit more

What's the voltage drop across the 1K?

For HK257 it should be only 10mA or 10V drop so zero resistor would be 2% higher G2 voltage and could go wrong very quickly.

4E27 appears to draw more G2 current and could have 100mA G2 current when plate is slammed. That may be a significant difference. Try 500. I do not think going lower will do good, and makes harm easier.

> I also have some asbestos jacket wire

YEAH MAN!!! Miracle Mineral, very appropriate technology.

[Willabe]

Oh, Come on now PRR,     My Dad --- Loved --- that stuff!           I remember he had a few BIG roll's of that "Mircale Mineral" stuff! They were at least, 4/5"s wide and 1/16" or so thick, must have been 25' or so long, each.   "Here Brad hold this, sure, OK dad"         yeah well..., It was thought to be safe, great, "Mircale" stuff, back then.

My parents/our family's lively hood at that time, was a 16 lane bowling ally (that dad had built) in the great, late... "50's/60's  "Hail, Richard, the King"  :icon_king:   Mayor Daley's" Chgo. In fact, we were the first atomatic lanes, (oh man, must of put some poor "pin boys" out of business) Brunswick lanes in Chgo! Life was good, "because business was good",(so I remember Mom & Dad sayin) factory's were running a full 3 shift's back then, in Chgo. the bars were open till 4 AM/5AM on Sat.(and still are) and at our place, "Bell Bowl" it was almost always 3/4 deep at the bar! Thats where the $$$ was!(so Dad said and I think he was right! Been to a Baseball or Football or Basketball, or what ever sports game latley? Last I heard, 1 beer at Wriggley/Cubes park is 6$   ) In the time it was  "Work Hard Play Hard" (or so they said/say), but that was a different time in America, so be it, no judgment on my part. The first 3/4 years they told me they  - Never! -  even turn'ed the lane's off!    

Remember what those maple bowling lanes & maple bowling pins were finished with in the 50's/60's , sure wasn't poly? Highly Flamable Nitro Lacqure (I've GOT to buy a dictionary!) Compleat with wood trussis for the roof and over the lanes a good 2"s of that wonderfull "Miracle" stuff, sprayed on to the ceiling for fire/sound control, was standard at the time.  Dad would bring home the old bowling pins home to burn in our fire place, took only one stick match to light them up, and I mean ......            :bom:           WOOOHHFFOOPOOPHFFFF                  !!!          YEAH!!!  FIRE!!!

Thats why he  ---  Loved  ---any thing that was "Fire Proof"!  Talk about --"Self Starting"--

Oh we had lots of fun back then, oil based paint, wash your self down with Terp's or good ol'e leaded gasoline and NOT just a few drops, I mean we washed up with it, and always  leaded gasoline to clean up after taring a roof!  

    I've gone on too long,


       Thanks,   Brad        

[sluckey]

I also have some asbestos jacket wire rated for 1000 degrees Fahrenheit.

Hmmm. That gives me an offbeat idea.   :idea1:

This amp might look good built into an old toaster oven, the kind with a glass door.

[DummyLoad]

This amp might look good built into an old toaster oven

ya kno, circa 1993-94 i saved a macintosh lisa computer from being turned into an aquarium - i gave the guy $20.00 for it - today, in the condition it's in, it's a collector item that will fetch around a grand or so... somehow i don't think that will apply here - u gots a toaster ta donate?   

[sluckey]

I bet Goodwill has one. I'll check while I'm doing my Christmas shopping.  

[Willabe]

ISOTone,

 :glasses9:    Tubes in the Dark!    Nice!

How bright is it? Does it light up the room enough to find your way around, like a night light? Looks pretty bright.

      Thanks,     Brad   

[DummyLoad]

well, some disappointing telemetry last night, buttery came over and helped with another shakedown cruise, so we decided to take some measurements to see what glo-champ is really putting to the speaker. i have a fluke 87 DMM which has a really decent true-RMS ACVM. under hard playing we could get about 20 VRMS across the terminals connected to an 8Ω speaker -that's roughly 50 WRMS balls-out distorted. ok, so let's see what she does clean... hooking up 100W 8ohm dummy load resistor we get around 11.4VRMS across the terminals driving @ 1KHz with a low distortion sine wave generator to about 5% output THD displayed by our trusty tek AA-501 analyzer. 11.4VRMS into 8Ω is about 16.4WRMS. i expected better than that - given that the documentation says 25W is tenable within our parameters, however, the docs do not mention a distortion figure so i'm assuming it's certainly to be < 10%. what may be happening is that that g2 resistor is too large, too large to the point that we are snuffing power. tomorrow, if buttery can make the time to help, we're going to try smaller R values for Rg2 and run things up slowly while monitoring Ig2, more to the point, the Pdiss of g2 at idle and slowly work our way up to wide open. another thought was that our driver stage can't cut the mustard and is distorting long before the 4E27 is making full power. well check that too - we are at -37.75V Vgk so we need ~~53VRMS into a 220k load from the driver to go to full power.

lastly, we were jubilantly able to rid ourselves of the test lead and alligator clip plate cap connection. we fabricated a plate cap/heat-sink out of 500mil dia. copper round stock and obtained some suitable test probe 18AWG silicone jacketed rated @ 150degC and 1000V. tomorrow we'll fabricate a temporary hardwood cap for the exposed copper plate cap. the only question remaining is what flavor of hardwood do we want to scent my lab with...

--ISO