Quieting Down a DIY 5F1 Champ(First my Son's Champ, now mine!)

[sluckey]

I may be wrong, but aren't the diodes connected differently on the first page schematic (which seems correct to me), than on the other pages (SERVICE MANUAL DOCUMENT  5/31/07), which seems backwards?

They're connected the same on all pages.

[dinkotom]

now I see it too   

[Platefire]

Hi Ya'll! I'm tagging on to this because of the valuable info and conversation contained.

My Champ quit! On inspection and a little voltage testing discovered my high voltage DC was stopping at the OT/6V6 plates. No voltage at screens and beyond, the 2 watt/10K was gone. Also after more checking found out the 8uF/450V cap for the screen had failed and caused a direct path to ground. I suppose the cap failed and took the resistor out.

So since I got to do a repair I decided I may as well upgrade a bit to maybe defeat some of the normal Champ hummm. So referring to the original plan I did to my Son's amp back in 2014, would like to do something similar. I will be using the 5Y3 rectifier---so where the upgrade plan used a 40uF before the 250 Ohm R and another 40uF after the 250R to plates. My thought was to use a 30uF in those two locations and maybe my 5Y3 could still survive? So the plan would be the Identical as attached sketch with the exception, the two 40uF's on sketch will be 30uF's/500V.

Thought I would run it by ya'll to see if there are any holes in it? Thanks, Platefire

[Platefire]

Since nobody responded to my previous post question, am I to assume that  it's correct, workable and and i should proceed with vigor? I feel pretty good about the plan, just concerned about the 5Y3's health. I think I remember sluckey said he had gone as high as 33uF with a 5Y3 without any problems. 

Come on sluckey, PRR, tubenit, Willabe----Please bless it or kick it in the head--I need to order parts!

  Platefire

[vibrolax]

I think I always use 33 uF right after the 5Y3, and have never suffered a failure.
Go for it.
Jon

[sluckey]

Bless you. My only concern would be the 250Ω/5W. May be too light. Measure the voltage drop ***ACROSS*** that 250Ω and do some math. Actual power will equal V²÷250. For example, you measure 25V across the resistor, so...

25² ÷ 250 = 2.5W actual power dissipated by that 250Ω resistor. Double that value for safety so use a 5W resistor.

So, if you actually have less than 25v across the resistor that's even better, but if you have more than 25v across the resistor better to use a 10 watt resistor.

If you don't want to do the math then just get a 250Ω/10W resistor to start with. 

[Platefire]

Doing the math isn't the problem, I don't have a 250 resistor to hook up and measure. I haven't ordered any of the parts yet. Guess I could order a 5 watt & 10 watt and which ever I need, use.

I know the voltage on plates is about 378VDC. Tried calculating voltage drop across the resistor but the answer doesn't make sense:

Current I=v/r=378/250=1.512 Amperes

Voltage across Resistor  V=I/R=(1.512)(250)=378V

Somethings hay wire? That formula shows no drop in voltage. Must of done something wrong. Platefire   

[John]

You're not dropping 378 across that resistor, or at least you shouldn't be. Sluckey said to measure *across* the resistor. The way you have it figured your amp is pulling 1.5 amps. No way! I haven't read the whole thread but it's a Champ, so should be well under 100 mA, or .1 amp (I think... 1 power tube, 1 preamp tube ) So anyway....


250r * .1 = 25 volts, so you should  be dropping about 25 volts *across* that resistor at the most.

[sluckey]

Guess I could order a 5 watt & 10 watt and which ever I need, use.

Since you must buy the resistor just get a 10 watter and be done with it. And when you mount the resistor give it plenty of air space around it. It will get hot. It's supposed to get hot. Keep at least 1/2" clearance around the resistor. Don't put your extra filter cap up close to that resistor.

When you get this mod done if you feel that your B+ is too low just put a 5AR4 tube in the rectifier socket.

[Platefire]

Thanks sluckey, to be honest I'm still having a debate in my mind rather
To go with the upgraded or go back with original set up. The hum never bothered
Me a lot and I sure love the tone and response. So if I go back with the same,
I know I won't loose any of that, but with the upgrade---I'm not sure.
Other than a quieter amp, what are the pluses for the upgrade? Platefire


BTW---the reason I'm deliberating so hard on this is I've been using the champ a lot
Lately and it's sounding so good, don't want to loose anything, if anything I want to gain some!
From my research the trade off might be loose a little responsiveness for a tighter bottom end?

[sluckey]

If you like the way it sounds leave it alone.

If you want to know how the sound is affected with the extra filter stage then experiment with it. Leave the original caps just as they are and add a 33µF cap and 250Ω/10W resistor between the rectifier and the board. If you like it both ways consider using a DPDT switch so you can switch the extra filter stage in and out. One way is original, flip the switch for the additional filtering. That's the only way you'll ever know how what you hear changes.

[kagliostro]

If you like it both ways consider using a DPDT switch so you can switch the extra filter stage in and out.

VOX do something like that on the AC30CC2 and call it Smoothing Switch VINTAGE / MODERN



Note the way they do it, using a resistor to keep cap charged

Franco

[PRR]

> VOX do something like that

Yes; but that is a fix-bias push-pull BIG amp and we are talking about a Champ (self-bias SE). The big amp sucks more when pushed. The Champ doesn't. "Sag" won't happen.

It isn't 370V across 250r. The Champ's bias makes it act somewhat like a resistor. If it is happy bias/load, it acts about like the audio load. Say 7K. So for a first easy-number crack, it pulls 350V/7K= 50mA. (Probably less.) 50mA or 0.050A in 250r is 0.625 Watts. Need >=2W part.

> just get a 10 watter and be done with it

Don't disagree. I just put a full 6.0"x6.2" post where I only needed a 3.5x3.5. However the 6V6 is a 12W-14W tube. We only want a little drop, not to drop as much as the 6V6. It is likely we don't need anything like 12-14W, even 10W. With math we find <1W, and do need a 2W part, so it is indeed a Power resistor and the 10W may be the same price? (I used the 6-by because it was already in the house and far cheaper than driving to the Depot for a lesser stick.)

[kagliostro]

Ciao PRR

> VOX do something like that


Yes; but that is a fix-bias push-pull BIG amp and we are talking about a Champ (self-bias SE). The big amp sucks more when pushed. The Champ doesn't. "Sag" won't happen.

I agree with you, an SE amp didn't Sag, only one thing, the AC30 is a Cathode Bias amp, not a Fixed Bias

and ... thinking to the option suggested by Steve, I remembered that VOX used on that amp a capacitor switch with a resistor between

the added capacitor and ground as to keep it in charge (no pops ?) with a switch that shorts the resistor to insert the function of the cap on the

circuit, my intention was to point the attention to the use of the resistor (if to add the switch + cap was the choice)

Franco

[Platefire]

Even though I'll probably not attempt the switching option between vintage and modern, I have been playing
With the switching arrangement how a DPDT might be hooked up to accomplish this. It's a good brain teaser! Platefire

[kagliostro]

........  how a DPDT might be hooked up to accomplish this

Something like this ?

Franco

[Platefire]

Thanks Franco! Looks interesting. My problem in understanding what
Your doing with the connections to the DPDT? DPDT has 6 terminals.
I only see 4 terminals on yours and they are not in the normal
Locations----so I can't really see the power flow in switched positions.
Platefire


Edit: ok I studied it a Little more and see. In one switch position the
Path around the 250 is provided and the path to ground on the 40uF is
Blocked by the 10k R---vintage. The other switch position the path around
The 250 is cut off and voltage must then pass through the 250 plus the
Ground connection is then connected to the neg lead of the  40uf.
That's pretty cool!


But! If I'm not mistaken, I think I found a routing of voltage through
The DPDT without having to mess with the ground. Platefire

[kagliostro]

Connections are six but only four are user

Ciao

Franco

[Platefire]

OK! The minuet sluckey suggested using a DPDT, I started working on a plan. Certainly not because I was sure I want to try to install it but, i though that was a pretty good puzzle to work out.

So this is just a rough sketch but it's doing all the voltages transfers through the switch. I was thinking, boy! if you did it this way, you would need a good heavy duty switch because if it shorted out you would have major smoke.

OK, so here it is, tell me if it's workable? Platefire

BTW---The hardest part of actually performing this from my end is trying to find a spot
to install the DPDT without stringing out the leads.

[kagliostro]

I think your scheme will work but is possible you have a pop when you switch, also there will be an inrush current when the 40uF cap is connected to B+

Not that I'm sure about my version, but with it I'm trying to avoid those problems

Here my version with the DPDT draw in one other way



Franco

[sluckey]

K, I don't like having B+ and ground on the same switch. Just makes me nervous. I prefer something like the attached drawing.

Plate, here's an idea. Just get a choke and convert to 5E1 schematic. Forget about any switch.

EDIT... Fixed pic IAW shooter

[shooter]

I don't like having B+ and ground on the same switch

+1

Sluckey, I did a small edit on the snipit, I think that's what you were going for

[sluckey]

Thanks! I never even notices that. 

[kagliostro]

I like that 


Franco

[Platefire]

Guys! I really appreciate your combining your tube amp skills together to come up with this plan, Great! I don't think such a thing as this has been done to a champ?? So I guess it's decision time for me--either put up or shut up:>)

I have looked into the physical aspect of this and I'm really thinking it is possible. If you will refer to my picture and my notes, I'll run my thoughts by on what I think can be done.

1-See the small board next to the main board? That was originally a Pentode/Triode switching setup that I never liked the operation so I used the space for switchable cathode bypass cap for V1b. The resistor on the left is not connected to anything can be removed and the 22uf/25V V1b switchable cathode bypass cap can be relocated and mounted on the switch. OK that clears the small board for this mod. So I think the 100K/1 watt could go on the left turrets and the 40uF on the right turrets of the little board.

2-The 250/10 watt. I think I could mount a terminal strip in between the main board and the small board for that.

3-The choke. I think the choke can be mounted on the front bottom of chassis between PT and OT with the wire access hole for the leads right below in line with the bottom of the small board.

4-The DPDT. There is 1 3/4 Inches between the 5Y3 and the 6V6. I think the switch could go centered between those two tube sockets.

So I think that's it, other than doing the hookup/lead dress as well as possible. I think the space can be eaked out to do it. Platefire 

[shooter]

I never even notices that. 

I only noticed cuz the sun got eclipsed

[sluckey]

Look closely at my drawing. Both resistors will mount directly to the switch. Look at how I mounted a 10W resistor on my standby plus mod on page 1 of this pdf...

     http://sluckeyamps.com/VAC15/Vox_AC15_mods.pdf

If you want the bestus of all, replace the 250Ω/10W with a choke.

[PRR]

_I_ don't understand why you would want to switch-out this mod. You don't want hum/buzz! (the axe gets enuff already.) The few-percent drop of raw power output is not going to spoil any show where you brought a Champ.

_I_ would clip-lead it in (carefully!!) and try both ways before committing to a switch and a hole.

Anyway, what is wrong with the attached SPDT solution? The 40uFd is not totally out of circuit but with 250r in line it isn't doing much. It does charge to full voltage for less POP when you flip switch with power on.

[shooter]

which way is standby?

[Platefire]

  I'm letting all this soak in a bit

[Platefire]

Well I made my decision. I decided not to go with the vintage/modern switchable arrangement.

I decided to up the vintage arrangement a bit to 22uF OT/Plates, 10uF screen and vintage original 8uF for preamp.

Hope you guys aren't to put out with me after all the hard work you did on the other plans. I appreciate your help! Just getting my Champ working again will be a thrill because I had been using it almost every day and kind off missing it. Thanks, Platefire

[leevc5]

You might look in to putting a 6L6 in his amp. It has been discussed on this forum in the past. As I recall the conclusion was that a 6L6 can be swapped for the 6V6: it will provide more clean head room and wider tonal response; It will not increase the output by much if any and it will not have the same tone as the 6V6 (if that is good or bad will be in the ears of the beholder).

[Platefire]

Yes, I have ran a 6L6 in it. When I built the amp it was designed with a PT with enough heater amps to handle a 6L6, so the first few years that's all I ran in it. Later on I tried a JJ 6V6 and I liked the tone and response a lot better. I also got a plug in SS rectifier I tried and ran with it. To me the thing just sounds awesome with the 5Y3, 6V6 and 12AX7. The original Champ hum never bothered me that much but for my Son it was intolerable, so we upgraded his as on the beginning of this thread.

I guess I'm kind of funny about my DIY Champ being my first amp build 17 years ago and I have been very happy with its performance, so it's not a whole lot of incentive to do much different. If it was just another project amp that I was throwing stuff at just to see what happens, it would be different.

I do think this thread may be very beneficial to someone down the line who is looking to do something like this to their original champ circuit, who do a search, then find these power supply circuits and try them. I hope when they so, they share their results. Platefire

BTW--These first Champ projects was brought about by an amp man known on the net as "Casey4s".
Some of you may of heard of him. He encouraged me to build it, that I hesitantly decided to take it on, he then hand built the kit, provided detailed instructions, provided e-mail communications through the whole process that included not only building the amp but the cab to. So he also provided the same thing for my Son's Champ. So these amps are good as they are because I got started on the right foot by Casey4s.
 

[leevc5]

I agree:
there is a lot of outstanding information on this thread. It would make a nice article for publication if the information were organized;
the sound of a 5Y3, 12AX7 (in fact I prefer a 12AY7) and 6V6 in the 5F1 format is about the best there is.
I have built five of these amps. I have found the ones using turret boards typically have more hum than the ones using circuit boards. I think the wires between the turrets act like little antennas picking up stray stuff that finds its way into the signal.

[Platefire]

I've been running my Champ in parallel with my converted
Bogen CHB 20A in 1-10 cab. It's not stereo but just a big &
wide sound. I set the Champ fat/thick and dial up the highs
On the Bogen. So I set the Champ volume like I want and
Then bring the Bogen up to balance with it. That is the most
Satifying sound to my ears. I'm anxious to get the champ going
Again. Just the right power level for my home playing. Platefire

[Platefire]

Need some help, re-thinking my amp failure. I thought I completely understood what happened based on this:

1-First I determined the first 10K power resistor between plate/OT and screen failed because is was open.

2-I attempted to clip in a new resistor around the open resistor to see if the amp would start working. When I did this the clipped in resistor started smoking, so I quickly shut it off.

3-I got to checking with my MM I finally found that the filter cap on the screen was completely closed to ground because I could get continuity with my MM from the positive pole to the negative/ground.

4-So this was a "Ah Ha" moment. The cap failed and took out the original resistor and was smoking my new test resistor. That was my analysis!

So tonight with parts ordered, I decided I would take the old parts out in prep for installing the new parts. So when I pulled out the failed 8uF filter cap, I checked it with my MM and it was not closed or no continuity from positive to negative like before??? The amp had 378VDC on the 6V6 plates in it's failed condition, all heaters were working but no voltage downstream to 6V6 screen or to 12AX7.

So I wondering, could the cap test failed one time and seem OK the next? Is there something else that could cause the resistor failure? Don't think there was a short anywhere else. This is kind of blowing my mind, because I thought I had it figured out. Platefire

[sluckey]

You fell for the old obvious culprit trick. 


With cap still out... Check resistance from 6V6 pin 4 to ground. Does it read low resistance? If so, pull the 6V6. Does the socket pin 4 still show low resistance?

[Platefire]

No. Shows .4 Ohms with tube in and 0 Ohms with it out. Platefire

Just testing the tube pulled out of the socket, I have continuity between Cathode pin #8 and Grid #2/screen pin #4.

Soooo--That's how I got continuity on both ends of the 8uf filter cap, it was shorting internally in the tube through Pin #4 tube screen to cathode pin #8 to cathode resistor/bypass cap to ground.

Just de-soldering and lifting one leg of the 25/25 Power tube Cathode bypass cap---the 470 Ohm cathode resistor then measured 466 Ohms(OK) but the cap had continuity from positive to negative leads. So apparently the 25/25 cap gave up the ghost and provided a path to ground. 

Boy! this one sure made a Monkey out of me not the first time and probably won't be the last!
Thanks for your help sluckey.

In actuality, if I had my original analysis was correct(instead of incorrect), I could have replaced the faulty 25/25 cathode bypass cap, the 22K 2watt resistor and the 6V6, and it would been good to go. Guess it's not a bad thing I'm installing new filter cap and power resistors, it has been 17 years. Looks like I ended up going around Robin Hood's barn on this one. Platefire

 
 

[Platefire]

Good news, my parts came in this morning and are installed. I'm running
my EH 6L6 that I was running before the now dead JJ 6V6S. Plate voltage is
376, screen 334, to pre-amps 292, 12ax7 plates 198 each. Sound good
and a little quieter!


Thanks sluckey for pointing the right direction on my trouble shooting.
Glad to have my Champ back up! Platefire

[PRR]

> Shows .4 Ohms with tube in and 0 Ohms with it out.

Zero? Or Infinity? They are different.

[DummyLoad]

nice! glad to read you got it sorted out.


--pete

[Platefire]

PRR----I was just trying to provide the answers/readings he ask for. In the
Process I just discovered my tube had a short. Yeah, my terminology
Is probably way off.


Thanks, Pete! I been jamming with the EH 6L6 in it but I'm missing my
JJ 6V6S---hafta get one ordered. Platefire

BTW-Here is a updated schematic of the Champ--may have mistakes!

[Platefire]

I was complaining about missing the old JJ6V6S that shorted out but----------Man! This amp has got a great clean sound like never before since making the changes and using my old EH 6L6. Platefire

[sluckey]

A working amp usually sounds better than a non-working amp.   

[Platefire]

Har! Har!  you let me off lite! Thought for sure you was going to bring up something about running a 6L6 on a 470 cathode resistor, but since you didn't, we'll just let that slide------

[Platefire]

Just thinking out loud, maybe no action here but----since my 6v6 failed with an internal short from screen to Cathode, I keep thinking of adding a screen resistor. I've been reading up on it some.

I've read the higher you go, the more it sucks tone. Some say install it 5watts or more so it won't fail. Others say make it 1watt because you want it to fail and act like a fuse.

I've also read that fender originally installed them because screen voltage was running higher than plate voltage and installed them to prevent Parasitic oscillation.

So my main interest is protecting my next 6V6 and maintaining tone. I'm hesitant to change anything but need to put the screen thing to rest--any Wisdom here? Platefire 

 

[Platefire]

Since my tube failure and damaged parts, I'm a little concerned with bias of the EH 6L6 I'm now running. It does feel very hot to the touch. So I calculated tube dissipation on this one to see where I am at. Let me show you what I did, and then I have a question?

I've got an old EH 6L6 from Doug in 2001 but the data sheet I found on it says maximum dissipation is 30 watts. That data sheet is attached.

Voltage Readings:

Plate voltage=382
Plate to Cathode=325.4
Across Cathode=34.64
Cathode 470 Resistor=466

V/R=34.64/466=.0743A=74.3mA Plate Current

(325.4)(.0743)=24.18 Watts Dissipation (80.6 %)

Normally it is recomended 70% Dissipation. It's my understanding the Class A can be biased a little hotter that Class B or AB.

So my question is(if my math is correct) am I safe in leaving it a 80.6%??? Platefire

[sluckey]

Plate voltage=382
Plate to Cathode=325.4
Across Cathode=34.64

These voltages don't add up. At least one of these readings is wrong. If your plate voltage is 382v and your cathode voltage is 34.64v, then plate to cathode must be 382 - 34.64 = 347.36. Yet you say it is 325.4. So, somethin ain't right.

Normally it is recomended 70% Dissipation.

That 70% is recommended for fixed bias amps. It's OK and quite common to run cathode biased amps at 100%.

[Platefire]

I got my data incorrect. It is 382 at the A node to OT but 360 on the
Plate. So 34.64 + 325.36=360. So that should straighten that out. So
I'm good to go at 80%------good! Platefire

[shooter]

good to go at 80%

fwiw, I've found on many SE builds 80% is where the PA comes alive, with big bottles, something north of 90%

it's pretty easy to do some math and || R's to the cathode R for "fine tuning"