It is currently Mon Mar 16, 2020 8:30 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4  Next
Go to page Previous  1, 2, 3, 4  Next
Author Message
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 6:40 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Where did you get the EC VC schematic ?

You gotta be in with SLOWHAND (as in Clapton)! Sorry didn't mean you slowhand :lol:

Really, I can't imagine the EC VC being much different than the original VC. Fender would be CRAZY to mess with that circuit. Even CBS knew better (at least for most of the 1960's and 1970's).


:mrgreen:


Last edited by BMW2002Ti on Fri Dec 28, 2012 3:41 pm, edited 1 time in total.

Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 6:56 am
Offline
Hobbyist
Hobbyist

Joined: Thu Oct 25, 2012 5:26 pm
Posts: 4
BMW2002Ti wrote:
Really, I can't imagine the EC VC being much different than the original VC. Fender would be CRAZY to mess with that circuit. Even CBS knew better (at least for most of the 1960's and 1970's).

At the opposit, they based this from from the pre-CBS champ, the tweed Champ 5F1 which has a completly different tone circuit and sounds much more midrangy (because of the tone circuit and the transformers). The marketing of the EC Vibro Champ says that it is a power stage vibrato, which was not the case on the original VC. So I'm just curious. The same for how they wired the attenuator switch.

I know the different ways of wiring such features, but I was wondering which ones Fender deciced to put in this particular amp.


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 7:24 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
slowhand73 wrote:
...Where did you get the EC VC schematic?...


I requested from Fender consumer relations via email. They sent an email with PDF.

http://www.fender.com/support/articles/contact-consumer-relations

After viewing the schematic, it was clear that the EC VC is Cathode biased, and signal modulated tremolo, not the "power stage tremolo" (bias wiggle) as stated in the description. While we're at it, I would also like to see the correct use of the terms "vibrato" and "tremolo", as vibrato is what is actually on a guitar, and tremolo is actually what is on an amp. Vibrato varies pitch, tremolo varies signal strength. :!: :x

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 7:40 am
Offline
Hobbyist
Hobbyist

Joined: Thu Oct 25, 2012 5:26 pm
Posts: 4
Thank you !

shimmilou wrote:
While we're at it, I would also like to see the correct use of the terms "vibrato" and "tremolo", as vibrato is what is actually on a guitar, and tremolo is actually what is on an amp. Vibrato varies pitch, tremolo varies signal strength. :!: :x


Yep, you're right. It is written in evry history book about the Fender brand that Leo (Fender) misused the two words.


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 9:36 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
The 5F1 didn't even have a tone stack circuit. I have reverted many VC's back to 5F1 standards. Part of the mod is bypassing the tone stack completely. Changing the GNFB resistor to 22k-ohms. And dropping the plate voltage to the input 12AX7.

With the vibrato/tremolo section intact, you get a bit more bite and gain with the modded VC versus the standard 5F1 tweed (due to extra 12AX7). I've compared them side-by-side. I'm lucky I have all three. A SF Bronco with the tone stack OEM intact. A BF VC with bypassed tone stack. And the 5F1.


5F1 circuit:

http://www.webphix.com/schematic%20heav ... _schem.pdf

And I'm almost certain that the vibrato/tremolo circuit of the EC VC is based on a separate tube oscillator and not an output tube bias wiggle. It puts the wiggle onto the second half of the input stage 12AX7's bias current. As no SE amp I know of has the vibrato/tremolo wiggling the cathode tied resistor/bypass cap or grid-to-ground resistor on the output tube.

AA764 VC with wiggle one second half of input 12AX7.

http://www.webphix.com/schematic%20heav ... _schem.pdf




Image


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 12:59 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
EC VC schematic:

Image

Sorry for the size. The next available down was too small. :lol:

_________________
Bill

Image


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 3:02 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Bluesky, a few observations. :)



1.) Basic schemo of input to output sections are similar to original BF and SF VC (AA or AB764). Except that the tremolo/vibrato seems to be wiggling the Screen grid of the 6V6GT?



2.) Notice BIG differences in PS section? That crazy CL-60 (NTC current limiter) --- Boy, Fender musta bought a truck load of these things and put them into EVERY new amp & other units --- :lol: :lol: :lol: --- and the solid-state diodes (D1 and D2) across the 5Y3GT, effectively eliminating the "sag" or tube nature of the 5Y3GT rectifier.

I'd bet this amp would sound much better with a good NOS 5Y3GT. And bypassing those crazy superfluous solid-state devices. If someone had this amp.... try a GE or RCA 5Y3GT or better yet a mil spec 6087 and run parallel bypass lines across that CL-60 (before the PT) and across those two SS diodes before the 5Y3GT. And try the amp out. IMHO... in a good amp design with quality components -- these are not needed. They only add noise and choke the performance.


http://www.ebay.com/sch/i.html?_nkw=6087+tube


It would be interesting how this amp would sound after this "breadboard" experiment (chucking a few ss parts).


3.) BTW... IMHO... C8 (0.1mfd/250VDC cap) is a fire hazard! :!: :?: :!: One should NEVER put anything rated under 600VDC across the live AC line (I use 1KV+ rated film caps). I have no idea what this cap is doing, except re-enacting the old "death cap." WTF?

http://www.audiobanter.com/showthread.php?t=40517



4.) If Fender wants to make a more "reliable" amp than the old AA764 VC (and that is impossible)-- there are much more sound ways of doing this. Like forget the 5Y3GT, if you can't find a good, new one (and you can't). Go to a FULL WAVE SS-bridge. Forget the CL-60. Use a good PT and UF4007 SS diodes.



5.) AND not use a fuse on the SECONDARY's CT (F4). A good PT doesn't need this. It could hurt the response of the amp to transients. READ: unecessarily pop when the amp is cranked. I wonder what kinda PT is in this amp. My bet --- not made in USA or Canada.

F2 & F3? Uh... This amp must have the cheapest tubes. Or designed by the most conservative engineer on Earth. If the tube's heaters are that weak that they need a fuse to protect their heaters... something is very wrong. This is supposedly a "boutique" guitar amp --- not an amp in a starter Rogue guitar/amp kit. How many Trainwrecks or Matchless do you see with this many fuses? And on a 6-8 watt SE amp?

Are the heater lines on the circuit board tracings?


6.) If Fender is so worried about protecting the circuitry of this amp --- esp the board -- put a dang fuse in the output stage. ESP on B+ to the 6V6GT & the OPT. This is where most users muck-up a tube amp.

Other than that no other issues with the circuit. :mrgreen:


Last edited by BMW2002Ti on Fri Dec 28, 2012 4:11 pm, edited 2 times in total.

Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 4:07 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
BMW2002Ti,

The diodes on the rectifier will do nothing for the sag, they are in series with the tube rectifier, and really will only function if the tube shorts, then the diodes will function and prevent AC from getting through. If you think about it, if two diodes were to be in series with each other, only one would block current in the reverse direction, not allowing the other to even "see" the reverse voltage. In the case of the tube rectifier in series with the diodes, the diodes don't play a part in the rectification at all, they are just there for protection against AC in the case of a rectifier tube short, nothing more. Since the tube is the only part that actually rectifies during normal operation, there will still be as much sag as when there are no diodes there.

A fuse (F4) has zero affect on the sound of the amp, and certainly will not cause pops or other noises during normal operation, it's only purpose is to prevent more damage should a tube short. As for F3, have you seen what happens when a tube shorts internally to the heater and takes out the heater supply? F3 and F4 fuses are a good idea, fuse blows indicating a bad tube, no more burnt resistors and wires in the heater circuit or in the power supply, zero affect on amp sound. Unfortunately, a fuse on the speaker output section will do absolutely nothing to protect the amp in the case of a shorted tube.

Almost forgot, the output of the tremolo tube is the Cathode, not the Plate. The Cathode of the trem tube is tied to the Cathode of V1B to "wiggle" the DC voltage at the Cathode of V1B.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 4:25 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Shimmy,

First off, thanks for the schemo.

I beg to differ. Those diodes directly effect the ripple effect of the PS. And the recovery time (time-constant) of that 5Y3GT. It's a common trick used in vintage amps --- with owners that can't afford or find NOS tube rectifiers. See valve Wizard's explanation:

"If we were worried about running a valve rectifier too close to its maximum Va(rms), we could place one or more silicon diodes having a much higher PIV in series with each anode as protection elements. In theory the valve rectifier can then be used with supply voltages up to twice the rated Va(rms). The silicon diodes will have no adverse effects on the normal operation of the valve rectifier.

The valve type used will depend on the current you need to deliver, and the maximum ratings are given in a graph on the data sheet.
The EZ80 is rated at between 90mA at 350Vrms, to 104mA at 100Vrms
The GZ34 is rated at 250mA at all supply voltages.
This refers to the average anode current. The peak anode current will be higher but is only allowable for short current transients."


Edit: they do effect the tone (IMO). The sag is less. Headroom is gained by seemingly decreasing the sag voltage/current --- I don't like them on guitar amps. Though they work well on hi-fi amp.

http://www.valvewizard.co.uk/fullwave.html

( Half way down the page ).

And this famous Dynaco ST-70 modification for using Sovtek 5AR4 in those amps:

http://www.audioasylum.com/audio/tubes/ ... 48330.html

I am not an advocate of fuses to cover up poor components or circuitry. That many fuses on the PT suggests a poor PT. Not saving the owner grief. Because, if any blow, he would most prolly need to take the amp to a tech to get it fixed. And how many techs are just going to replace a fuse? And not the PT? I wouldn't, at least not without going through the WHOLE amp to see why the fuse popped in the first place.

And that cap across the AC line is a definite indication that the amp was not designed by an engineer who knew what he's doing. So, this doesn't bode well for the rest of the amp.

Sorry, I'm old school about any tube amp.

Edit: Hey! What about that trem wiggle on the screen? Ever seen any amp with this setup?


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 4:51 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Totally different, as the valve wizard is talking about the PIV that the rectifier tube would see if using a higher AC supply voltage. Using the diodes with a high PIV rating would allow the use of higher supply voltages to the tube. In that case the diodes higher PIV rating will protect the rectifier tube from the larger collapsing field of the transformer, as the diodes block the field collapse from reaching the rectifier tube. The diodes in series with the rectifier tube do not function as rectifiers unless the tube shorts. As the site that you linked states; "The silicon diodes will have no adverse [a]ffects on the normal operation of the valve rectifier." In other words, you will still have the sag because the diodes in this case are not rectifiers during normal operation.

Really, what would be the reason to use both diodes and a tube for rectification, other than the diodes for protection? If the diodes were rectifying, and they affected the sag of the tube, there would be no reason to use a tube at all. It's much cheaper and easier to use solid state rectifier instead of a tube and it's required circuitry and increased current demand on the PT. :wink:

Edit:
BMW2002Ti wrote:
...Hey! What about that trem wiggle on the screen? Ever seen any amp with this setup?


It looks to me that the "wiggle" is from the Cathode of the trem tube wiggling the Cathode of V1B. Am I seeing that wrong? You won't get much wiggle on the screen supply, which is also the supply to V1B Plate. And no, I haven't seen anything like it before....weird. I haven't heard one either, but the claims are that it is an intense tremolo effect.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 5:33 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
I really have no comment on the design of the amp. I just happended to have the schematic handy and posted it. Personally, I'd rather have a straight 5F1 Champ instead of this bastardized thing. I have no use for, nor do I even like tremolo. 8)

_________________
Bill

Image


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 7:03 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Bluesky & Shimmy,

1.) That tremolo/vibrato C+ seems to connected (dot) to the screen and not V1B of 12AX7. The ground (which does have resistors) is connected to the V1B. Maybe this is the bias-wiggle.

2.) There is no reason to have a 5Y3GT, if you are going to have "sand" components in the power supply. A good UF4007 bridge with GOOD 500VDC caps will be a lot more reliable and stout.

Just my 2¢ worth, of 2¢...


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 8:15 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Yes, the Plates of the trem tube are fed from the same supply as the screen, but the Plate of the trem tube is not the output of that tube half in this case (note that the screen supply voltage feeds both Plates of the trem tube). It looks like the output of the trem tube is a Cathode follower, using resistors to lower the voltage to match the V1B Cathode voltage, connected to the Cathode circuit of V1B, modulating the bias of V1B. I would think that the trem tube would have to pull some hellacious current in order to wiggle the screen supply voltage, and this would also wiggle the voltage to the preamp tubes Plates, and the oscillator half of the trem tube, so everything would be wiggling, and the trem tube would wiggle it's own supply voltage. The 12AX7 current isn't going to affect the screen supply voltage much, but if it could do it enough to cause a "throbbing" tremolo it would cause some noticeable distortion from the output tube when using tremolo.

Definitely a strange amp, but if it sounds good.....OK I guess. :|

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Dec 28, 2012 10:34 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Shimmy, you are correct. The anode is getting C+ from the same source as the screen for the 6V6GT. The original VC did not have a screen resistor OEM. This is a wise addition.

The wiggle is on the cathode bias of V1B. This is just like the VC (if I'd paid attention to the schematics a bit more). So, as far as the signal to 6V6GT sections are concerned --- the EC VC is much like the origina VC.

http://www.webphix.com/schematic%20heav ... _ab764.pdf


Top
Profile
Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Sat Dec 29, 2012 6:29 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
I didn't look at the ab764 either.

So, now we know why the EC VC is so expensive.......they added SGRs. :lol:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4  Next
Go to page Previous  1, 2, 3, 4  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: TimsAudio and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: