6L6 Champ (style) Build

[frankenxtein]

Thank you Platefire 

http://el34world.com/Forum/index.php?topic=9444.msg86674#msg86674

This didn't blow up did it? 

Had a hard time trying to figure out what to build with some Voice of Music VM714 Iron from 1958-59.
      I believe I have the same PT and OT Platefire has , it's just a hunch but I just saw a Stancor 138813 12558-1. on eBay   
  Mine is a Triwec Transformer (524839)  12558 (720VCT .060A) Wiring scheme ........ Pri 117VAC Black , HT red CT red/yellow , 5VAC yellow 1.8A , 6.3VAC green 1.3A , (6.3VAC gray 1A was used on the stereo preamp 1 tube.) 3-12AX7 , 12AU7 , 6E5 , 6V6GT , 5Y3GT
 VM714.710A, 711A , , my OT is a Stancor 12559-1. 5300 ohms x 32 and 8ohms.

edit: on the VM714 OT Black went to cathode , Green to Ground , Yellow 8ohms. a 6-8 ohm 6x9 + 14ohm tweeter

on the VM733 the green went to cathode , black was ground , yellow 4ohms (speaker is 3.2ohm) I had a whole unit ........ It's parts are spreading out here still lol
I'll provide a ratio on these OT's soon.
The  Tube amp power current draw calculator , it sure hits right at the OT load impedance when you use a 6L6GC. The current draw is over . Calculated current: 89.16mA at 5501R calculated load (10% plus factored in)
          I'm not looking for any kind of power just an amp that will function , another simple amp. 12AX7-6L6-5Y3 trying to keep the iron together.
 ............................................................
I haven't got a schematic yet , gonna need a bigger cable box lol. Just a tone , volume , brightness/bypass switches. Point to point. I'll make a chassis for this one , although it would look good in a Olive Green Toaster, That might be kinda cramped. 

[pompeiisneaks]

You really are the frankenxtein :) Sounds adventurous and I'd love to see pics :)

~Phil

[frankenxtein]

You really are the frankenxtein :) Sounds adventurous and I'd love to see pics :)

~Phil

Thank you 

 Realizing this is all pretty laughable to folks that build really nice big amps , using multiple EL34's

I'm wondering whether to go with the Sovtek 5Y3GT or the JJ 5Y3S. Also the Sovetek  6L6WXT+ or the JJ 6L6GC ?  OT load impedance 5300 ohm.
I've read the Sovtek 5Y3GT wont drop the voltage? Maybe a good thing for keeping the voltage up on the 6L6 ?
The JJ6L6GC I also read is smoother compared to the harsher Sovtek 6L6WXT+?
 Since I'm sticking to lower priced tubes ...... Might as well consider the Sino 6L6WGS , 6L6EH

[pompeiisneaks]

From what I've understood, the quality is pretty close, sovtek is made in russian factories and JJ in slovakian, but some people do tend to go off on JJ.  I'm not sure I've had a bad one yet, but I'm newer to the build ing side myself, and my other tube amp had fender stock in it.

~Phil

[frankenxtein]

This amp will probably belong to someone else in the end and they probably wont have a bucking transformer.  (There's an item a amp builder could make a buck on) 

[frankenxtein]

Well I had fun making a chassis 13.25" x 7.25"  , that IEC hole will keep somebody up at night.   

Used a 12" x 18" piece of 26ga galvanized about $5 at Home Depot It's fairly sturdy , the PT has a tapped plate I'll put on the underside to stiffen it up.

I guess I'll go with JJ's ? Ceramic sockets because I have a 9pin and a 8pin already. I like the preamp I've been using in the Deluxe Micro minus the MV so building the power section is just a Champ ? I was going to go with 22-22uf500v first two. That last cap I have a 8uf 450v Atom. I've been reading people were just putting a 6L6 in a Champ and changing the bias resistor and using a 25uf 100v bypass.   

[pompeiisneaks]

I actually tried making a chassis out of galvanized and man it was too flimsy.  (my first build ever, a Vox AC30).  From then on out I've always bought chassis'.

~Phil

[frankenxtein]

 That extra brake , well really the first brake that little one ends up on the bottom edge , makes em strong. Like "C" channel. If I had a press brake you could probably stand on it. It's pretty stout actually , stiffer than any of the single brake aluminum chassis in most of these old tape decks. I'm not going to stand on it but it crossed my mind.  I'm surprised it came out as good as it did. It's kind of big but hey I just cut the corners out of the the 12x18 piece of steel 4 small screws and nuts. Making it smaller would be harder to work up anyhow. It's handmade   
     
       What's puzzling me is the math with OT ratios.
The VM-714 (one in use here) 9vac on the primary gives .35vac on the secondary.

    9 divided by .35 = 25.71 x 25.71 = 661.0041 x 8 = 5288.0328
I guess I should round off the numbers , heck I might be doing it wrong. 

[PRR]

> OT ratios. ....  9 divided by .35 = 25.71 x 25.71 = 661.0041 x 8 = 5288.0328

5,200 Ohms, 5.2K, is a perfectly reasonable primary impedance for loading one 6V6.

Rounding as 5.3K doesn't make any difference.

[frankenxtein]

> OT ratios. ....  9 divided by .35 = 25.71 x 25.71 = 661.0041 x 8 = 5288.0328

5,200 Ohms, 5.2K, is a perfectly reasonable primary impedance for loading one 6V6.

Rounding as 5.3K doesn't make any difference.

Thank you   

I got my Variac today and I'm going through the latest additions to the junk yard. Terrible color schemes on these things.  Green Yellow Black and different on many from one model/year to another. This VM714 OT has the same measurement .....  Using Black Yellow (1.8ohms .13mH) as using Green Yellow  (1.ohm .10mH)
 Feeling a little better checking these things out , interesting article ....

 http://education.lenardaudio.com/en/14_valve_amps_5.html

[Willabe]

(There's an item a amp builder could make a buck on)

They make them.

[frankenxtein]

Getting everything laid out out here.
5y3-6l6-12ax7
I have two 6.3vac  1.3A and 1.A , no center taps , long leads
 
Would there be any advantage to having a separate 6.3 winding for the preamp tube in this SE? Less noise?

Would it be better to run the two tubes off the same tap and just coil up that extra winding? I'll put a lamp in it for start up but ...... I've taken to not leaving one in the little amps. Plan on making up some LED lamps (lower draw on the heater winding) 

They had a single 12ax7 (stereo preamp) on that 1.A winding.
If it was an advantage  ..... 2 artificial CT's?

Making artificial CT's  , would that be better to have it near or on the valve?

I'm not trying to over engineer this Champ (Champ for reference purpose)

I usually put the artificial CT back in the Power Supply section and run the 6.3 from valve to valve. I only build 2 tube amps , I don't usually have problems with hum.

I planned on running the heater to the 12ax7 in the back edge of the chassis instead of my up in the air over everything lol.

The PT kicks out 427-0-427 unloaded.

To answer my own question ........ 

Seeing the 6l6 can nearly take an amp itself , I'll be using the 1.3A for it alone and letting the 12ax7 have the 1.A 

Doing the CT's at the valves or close by 

[frankenxtein]

Kind of where I'm going with this ...... see hacked schematic  and Donor PT-OT original body .... er design schematic. 
 They have a 500ohm 5W first resistor after the first cap in the VM-714 PS.

 Do I want that heavy of a resistor ? 

I expect this PT to kick out what's in the VM-714 schematic.

Again I'm not seeking a powerhouse ..... but the higher voltage makes that 6l6GC work with my OT?  Moving around /switching a few tag strips. Got the AC hooked to the chassis it's much neater than previous builds. Nice having a 2" tall chassis. I've never hooked up a 5y3 rectifier .......

[Tony Bones]

Looks good to me!

As for the power rating of the cathode resistor, you can figure that out for yourself.

P= IV = I^2 / R = V^2 / R
P= IV = I^2 * R = V^2 / R

To decide if 5W is big enough, calculate (or estimate) the maximum current through or voltage across the resistor. One way to find the maximum current is by using the 30W max plate dissipation of the tube. Take 360V plate to cathode as a round guess to figure out the maximum allowable current through the tube, and hence through the cathode resistor. Use that to calculate the power dissipation of the resistor. Maybe double that for safety margin, especially if the resistor doesn't have a good way to shed heat. (It's heat that burns resistors, not current. The current creates the heat, but if you can move it away from the resistor to keep it cool, then it will handle more current.)

This is all just rough to see if a 5W cathode resistor is big enough and if everything else makes sense. It's worth understanding how to figure this kind of thing out for yourself.

{Edit: corrected equation per Tony's later post -PRR}

[sluckey]

P= IV = I^2 / R = V^2 / R

You really mean P= IV = I²R = V^2 / R, right?

[Tony Bones]

P= IV = I^2 / R = V^2 / R

You really mean P= IV = I²R = V^2 / R, right?

Yes, of course. Thanks for fixing that! 

[frankenxtein]

P= IV = I^2 / R = V^2 / R

You really mean P= IV = I²R = V^2 / R, right?

Yes, of course. Thanks for fixing that! 

er ... that was the day I skipped school ...... I'm afraid the furthest I got was goesinta's 

I honestly had not considered the wattage of that resistor  I've got a few 5watt here. May have to rig something up till I find the right one. It takes a day or two to get anything I need here in Memphis. Scary eh?  When I figure out the Bias I'll order a 10watt for it .... running low on tag strips anyhow. I appreciate the advice and any tips.

[HotBluePlates]

Again I'm not seeking a powerhouse ..... but the higher voltage makes that 6l6GC work with my OT?  ...

Let's imagine you don't want to stick to only 30w 6L6GC's.  23-25w seems a safe estimate for 6L6GB and similar (idle dissipation).

...  Mine is a Triwec Transformer (524839)  12558 (720VCT .060A) Wiring scheme ........ Pri 117VAC Black , HT red CT red/yellow , 5VAC yellow 1.8A , 6.3VAC green 1.3A , (6.3VAC gray 1A was used on the stereo preamp 1 tube.) 3-12AX7 , 12AU7 , 6E5 , 6V6GT , 5Y3GT ...

If the quote above means the original iron powered 1x 6V6, I don't hold much hope it'll let a 6L6 push any more power than the 6V6 did.

We don't know exactly what your B+ will be, much less the bias.  720v CT means 360vac per side; you mentioned "427v unloaded" earlier but I don't know if this was a.c., pulsating d.c. or what.

But 360vac * 1.414 = 509vdc, minus rectifier drop.  Wall voltage will be higher than the specified 117vac, you'd need filter caps rated for 600vdc.

Right there, I'd probably stop and look for other PT's.  I'd like to have 650v CT (325-0-325v) or less for a single-ended amp, but that's my preference.

But let's guess you press ahead.  25w / 500v = 50mA.  First-guess SE load should be 500v / 0.05A = 10kΩ, double what you have.  If you only use ~5kΩ, you'll get (0.05A² * 5kΩ) / 2 = 6.25w, so not "Wow!" power increase from a single 6V6.

Lower supply voltage would allow the same 12.5w from a lower OT load, but would also require more current.  Your PT is only rated for 60mA, and some has to be reserved for the 6L6 screen & preamp.

Triode curves for the 6L6 suggest 50mA plate current at around -45v bias (after adjusting for plate/screen voltage near 460v).  50mA plate plus ~5mA screen implies 45v / 0.055A = ~820Ω cathode bias resistor.  45v * 0.055A = ~2.5w, so you'll need at least a 5w resistor (or better, 10w).

[frankenxtein]

It's alive! 
Voltage 117vac (bucking transformer)
all new JJ tubes
397v B+
361v Plate
348v Screen
27.84v Cathode drop 538 ohm 2x270ohm 5watt
52mA current
17.3 watts dissipation

Probably could be improved a bit , nice full sound (no cathode bypass on the 6l6) , the 12ax7 is running around 181v per side just under 2v cathodes Put a bypass cap on the first side , boosts it up . The bright switch works good the tone control seems to have a good range of adjustment. 
Too late tonight to tweak it .... or early this AM to mess with it .... it's quiet.

I wasn't expecting anything beyond 5 watts ..... Tried to heat some leftovers with it , it just don't get hot enough. 

[kagliostro]

 


Franco


p.s.: I like the incorporated Amp Cradle 

[frankenxtein]

Franco


p.s.: I like the incorporated Amp Cradle 

It sounded pretty good and I'm taking a break to clean up the mess I made making it.

"Amp Cradle" .... I didn't know what one was honest  ... I thought it was another name for amp stand .... like on stage. I have two of those and they're just more weight and as useful as a sack of rocks.
              I thought building something to hold amps up while working on them would be ..... obsessive. People would think I was nuts ... lol. The 5y3 has to be vertical ..... probably good/better for any type of tube. I had been propping them up on end to check em out , bias that sort of thing. I'm not servicing amps (everyone breath) so some extra set of small holes in the top or the sides is what will be from now on. 
        With the costs of ending up with 2 Photofacts for this amp $23, the iron cost $27 add another $80 for the other parts.
       
         Building to fit a transformer  or two in this case was not cheap and it probably looks like crap on a oscilloscope. I'm certain I can make it function safely and be useful to someone. I stopped building until I had built a bucking transformer (I don't run any of em without) , then waited for a better 1000v VOM to start this and found I couldn't do it without the Variac , to check the OT's ............ what a money sink.

      It was fun and learned a bit more. I have a lot of reading to do , may need a choke or something to slow the powerup surge which is maybe 520v till everything pulls it down. The 500v F&T caps have to be better than electrolytic caps were back in the good old days. Rated for 500v they probably will take a bit more than that  

This power transformer was the same one used in another Voice of Music with a 6l6gb. It was a theory that the 6l6gc had the load impedance needed to work in a cathode bias amp. It looks odd with the giant tube and to quote manufacturer(s) & salesmen "This tube will replace any 6L6"  I've built a Silvertone 1471 12ax7-6v6gt-6x4 with a 40mA PT ..... never got warm and it's tiny OT wasn't stressed , that was before I had the bucking transformer. None of this junk I make is cutting edge .... they're all biased for endurance , for lack of a better word. They all will outlast me. 

       I'll figure out this one too. I read a lot of what is posted in the many threads here. Just learning to search it would give me the operators manual.
What's funny is technology hasn't changed much from the automobile radio. We probe it (got a temp probe on the new VOM) , dissect it , make it powerful , turn it into data but , in the end. ....... it's a car radio on steroids.  Enough rambling and forgive me if I make lite of what some people are everyone here is passionate about. The first real tube guitar amp I ever owned .... I built it myself ..... with a little help from everybody. I'm having fun aren't you? 
             
   

[frankenxtein]

Changed the cathode bypass to 680ohm
Voltage drop 30.5v
Resistor @ 677ohms
Plate     346v
Screen   330v
Plate dissipation 15 watts
Plate current  43mA

Made a cabinet for it ... scrap lumber , all solid wood except for the base which is MDF wrapped with 3/4" wood strip
15" wide x 9.75" deep x 9.5" tall
Steel mesh is from wastepaper basket

This amp is quiet and sounds great. Now it's within the right current draw.

[BetterOffShred]

Pretty cool Frank!  I'm glad you got it going the way you wanted, and thanks for posting the voltages.   I have a 6L6 ready for when I finally finish my Champ, they seem to run pretty good with a 6L6 if you have the juice to run one, and since the PT I'm using is for a pair of 6V6's I've read its good to go.  The cabinet looks good man, I really like the use of a wastebasket.  That's the ultimate "upcycling".   Good work all around dude.  You inspire me!
-Brett

[frankenxtein]

Pretty cool Frank!  I'm glad you got it going the way you wanted, and thanks for posting the voltages.   I have a 6L6 ready for when I finally finish my Champ, they seem to run pretty good with a 6L6 if you have the juice to run one, and since the PT I'm using is for a pair of 6V6's I've read its good to go.  The cabinet looks good man, I really like the use of a wastebasket.  That's the ultimate "upcycling".   Good work all around dude.  You inspire me!
-Brett

Thanks for the encouragement Brett. The juice current is what you let it have  , if I'm not wrong so ..... just because a valve will use X current. Doesn't mean it wont work with less. In this particular case biasing cold. Seems the norm is to run things close to the edge of a components tolerances. You don't have to run em hot. That said ...... I fail to mention the 12AX7 in this is running  200volts now. That really makes for a cleaner sound. Like a air bubble under a bumper sticker if you push it one way it goes somewhere else. This is all very interesting and I've only been doing this for a short time. What I'm doing might be reckless sometimes but , I don't have too much tied up in this particular amp. Instead of building to a design I'm fitting a design to the iron on hand. This little amp is almost as loud as my 5E3 Pro Amp. Good weather has me outside making cabinets. I'll get back to the PP amp soon and that one will be pushed closer to the limits. I've got to get back in this one to get the V1 numbers and provide a more detailed schematic so others can enjoy this particular design too.
Bryan

[shooter]

Doesn't mean it wont work with less. In this particular case biasing cold.

I basically only build SE and have found from about 85 -105% Pdis there is only small changes in tone, until you get to 11.  that's one of the parameters I tweak to the player.

[frankenxtein]

Voltage 117vac (bucking transformer)
 the 12ax7 is running around 181v per side just under 2v cathodes

Was trying to find that data on the preamp .... and here it was.

Also I was assuming I had 117vac (116.7vac) and last I checked it's 115vac.

Two volts may not be too big of a deal , but I want to be accurate/consistent.

[frankenxtein]

Doesn't mean it wont work with less. In this particular case biasing cold.

I basically only build SE and have found from about 85 -105% Pdis there is only small changes in tone, until you get to 11.  that's one of the parameters I tweak to the player.

I have very little experience building or playing with tube amps. Now that I have a few to compare to each other ....... it helps. This one needs to be cold (60mA HT) The V2 680ohm cathode resistor changed the V1 voltage +20volts. Just a theory but that is what changed the sound. I changed it once before but , wasn't checking the sound of it , just checking voltages/current.  Wasn't looking at V1 either , also , wasn't taking in to account these are all new tubes.

I wasn't expecting this amp to be more than the pumpkin it started out as.