Need help with building the right amp ( update)

[chikov]

Thank you guys for all your help. All week long I was refreshing my knowledge of the tube amps and circuitry and decided to build my own amp . Actually, i will build some classic amp, but I will learn how to voice it, bias it and customize it along the way. I still need some help... I would like to build an amp that uses just one input, may be two 12ax7 tubes, one phase inverter, two, push-pull 6V6 output tubes, Rectifier tube. I might start with Cathode biased Output stage, but later on, I would want to switch to grid biased one...
I have a couple of vintage tube amps where I will salvage some parts off... Which famous classic circuit with 6V6's would you recommend? I will do my own home work too, but may be some of you can suggest something out of your head highway. Thanks!
here are the amps:
[IMG:640:480]http://i409.photobucket.com/albums/pp171/alexjohnne/DSCN1330_zps89daf09f.jpg[/img]

I will be trying to ID all 5 transformers that are on the smaller one...

[xtian]

Fender Princeton (non reverb).

http://vintagefenderamprepair.com/wp-co ... Layout.pdf

[chikov]

Excellent, That points me in the direction of Fender type amp. I do not really want the tremolo, so I think I should go with 5E3 (Delux) circuit. I need to check the power transformers that I have and see if any of them will work. I need to find specs in them too.

[Phil_S]

You've mentioned the 5E3 more than once. All I want to say is that you should be sure it is what you want. The 5E3 circuit is very different from many others. If you don't want the tremolo on the Princeton, it's not a big deal to omit it.

[chikov]

I want to build 5E3 but with some modern upgrades that make it more reliable and with more head room ( so it would not go in overdrive too soon). Here is a cool article I found that I liked and I want to follow:
https://courses.physics.illinois.edu/ph ... deluxe.pdf

What do you think? My first newby question is "what is negative feedback loop for?"
Thanks.

[johnnyreece]

A while back, I did a blackface PR without tremolo or reverb (I know, it doesn't make sense to call it a PR if it doesn't have the R). The guy I made it for was pretty happy with it. Pretty clean amp compared to a 5e3. I can try to dig up the thread if you're interested.

Edit: Here's the thread: https://tubeamparchive.com/viewtopic.ph ... sc&start=0

[pdf64]

Here is a cool article I found that I liked and I want to follow:
https://courses.physics.illinois.edu/ph ... deluxe.pdf

What do you think? My first newby question is "what is negative feedback loop for?"

That paper seems to contain a lot of bad info (eg cathode stripping), bad practice (eg addition of a standby switch that hot switches a capacitive load on to a tube rectifier) and non-credible findings (eg plate voltage from a saggy 5Y3 HT supply does not change when cathode bias resistor is raised from 250 ohms to 430).

That does not seem cool to me!

Negative feedback reduces gain and makes the linear range of a system's performance more linear. See https://en.wikipedia.org/wiki/Negative_feedback

[DenDanger]

I built a home brew 5e3. I like it a lot. But it is a unique animal.
Mine has almost no clean headroom.(B+ a little low @350)
I think I would agree with the Princeton (6g2). It's pretty basic.
If you leave out the tremolo, close to the same amount of parts as the 5e3.

Denny

[chikov]

Oh my, thank you for warning me about the mistakes in that article. I started buying some parts already, but I will slow down...
I wanted to start with something relatively easy and then add on to it. I would like to use just the two 12ax7 for preamp, I like the idea of adjustable negative Grid bias, I like the idea of a Totem Pole before the stand by switch, I like the idea of using two extra resistors on the 6V6 screens. I want to have just the two inputs ( one single coil, one hum bucker). I like the idea of having the tone controls right after the first preamp triode (both bass and treble)... Negative Feedback Loop is a good idea - id like that. I do not want the tremolo, but I do have a spring can from an old Hammond Organ, so may be adding reverb in the future might be a good idea...
this schematic looks cool, but how do I get rid of tremolo part properly?
https://robrobinette.com/images/Guitar/ ... ematic.gif

[johnnyreece]

The one in the thread I linked is the AA964, if that helps. Might at least show you how to do what you're wanting to do.

[chikov]

The one in the thread I linked is the AA964, if that helps. Might at least show you how to do what you're wanting to do.

Thank you for your valuable advice. After i reread your thread 5-6 times, i decided to build it as well. I will have several questions along the way, but the easy one is this: what is the difference between 7025 and 12AX7 tubes?

[martin manning]

7025 is basically a low-noise version of 12AX7, particularly with regard to heater hum. IMO, only a fanatic would be worried about the practical difference.

[Firestorm]

If we're speaking of vintage tubes, the 7025 had spiral filaments to reduce hum. When the 12AX7A was introduced, it did too. You'd be hard pressed to find a modern tube without a spiral heater (except maybe Sovtek 12AX7WA/B/C, but I'm not certain.

[chikov]

I've got a minor set back. As I mentioned before, I was going to use Vintage power transformer from either two of my old Seeburg receiver amps. Well, the first one had a good B+ voltage (about 760V) but no 6.3 filament heater circuit... But the other I just pulled tonight has 6.3 and 6.8 supplies, extra 125V coil, but only 560 B+...(280V to center tap). Does not seem enough for 6V6 tubes... Should I find an extra transformer that produces just 6.5Volts ( how many mAmps should it handle)?? or should I just buy a new one from antique electronics?

[chikov]

I just realized , if I want to have a grid based biasing on 6V6 I need to have a transformer with 50V bias tap, right?