Winter amp project

[SomeoneYouKnew]

 

I can't access the help files with the program, so I had to "wing it" somewhat. For the "load resistance" it asks for I assume it wants the primary impedance of the OT, in this case 6.6K or are they asking for the "Plate Resistance" of the tubes ?

I can't help on this one. The only resources I've used from them are the download for their tonestack calculator and their online tube data.

 

But I think they have a forum. Maybe you could get some help on the PS software there?

 

 

If I was gonna wing it, I'd figure the voltage you'll have for the plate supply and divide that by the idle current for the pair of 5881s. For instance: if you had 400v on the plates and wanted 40w out of the pair, that would be 20w each.

70% of 20w = 14w.

14w / 400v = 35mA (per tube)

400v / 70mA = 5.7k load (at the first filter)

 

You can do the same sort of thing for each section:

 

Screen voltage / total screen current for both tubes = load resistance on the screen supply.

 

For the preamp, you normally bias so you have about half the supply voltage at the anode. So a shortcut is to double the value of each plate resistor and add all of them in parallel to represent the load resistance on your preamp supply.

[Casey4s]

I have been searching for that damn inductor everywhere including Ampeg/Loud tech. The Ampeg was really nice to talk to but he has no spare parts, the boards are stuffed "overseas" and shipped here.

 

So the best I have found so far is this 100mH coiled incutor. So if I wire 8 of them in series it will produce the 800mH I need, and tap it as needed at 100,300,400mH, but will it cause me problems?

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220586068024&ssPageName=STRK:MEWAX:IT

[Zozobra]

How much difference would using a 1H inductor make? May be easier to source.

[Casey4s]

 

How much difference would using a 1H inductor make? May be easier to source.

 

 

I need to tap it 3 places, so even if I had exactly 800mH in one coil, I still need to tap it at 400,300,100mH.

[SomeoneYouKnew]

I have been searching for that damn inductor everywhere including Ampeg/Loud tech. The Ampeg was really nice to talk to but he has no spare parts, the boards are stuffed "overseas" and shipped here. So the best I have found so far is this 100mH coiled incutor. So if I wire 8 of them in series it will produce the 800mH I need, and tap it as needed at 100,300,400mH, but will it cause me problems? http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220586068024&ssPageName=STRK:MEWAX:IT

I dunno Casey. I honestly don't.

[Casey4s]

I think I found one... A guy on another forum is an Ampeg service center and he is ordering one from Ampeg, I guess you just gotta know who to call.

 

What a load off of my mind. I bet I spent 40+ hours researching that one part. Now I can move forward with this build and finish sourcing the rest of the specialty parts.

 

 

Thanks for all the help SYK. I am sure I will be asking more stuff as I get going.

[Casey4s]

My Inductor is in the mail and I should have that next week so I can do My active mid control.

 

I did finish the Active Tone Stack drawings this afternoon. Here's a scan of my schematic.

 

[Casey4s]

Here's the power supply at this point.

 

 

 

[SomeoneYouKnew]

Hey Casey!

 

Congratulations on scoring that inductor. How much did it cost? I doubt I'll ever need one, but I wouldn't mind having a link to your source, just in case. PM me, if you don't wanna post it in public.

 

It wouldn't hurt to add a bleeder to your PS. Maybe 2.2Meg across any one of your caps. At power-off it will insure all the caps discharge. Should take about 10 seconds to get down to relatively safe voltages.

 

Also, consider connecting the CT of your filament windings to a positive DC supply instead of ground. 50v or so should work fine. Even running AC heaters, if they are always more positive than the cathodes, you won't have emission from heater to cathode. This will reduce another place where hum enters the system.

[Casey4s]

 

Hey Casey! Congratulations on scoring that inductor. How much did it cost? I doubt I'll ever need one, but I wouldn't mind having a link to your source, just in case. PM me, if you don't wanna post it in public. It wouldn't hurt to add a bleeder to your PS. Maybe 2.2Meg across any one of your caps. At power-off it will insure all the caps discharge. Should take about 10 seconds to get down to relatively safe voltages. Also, consider connecting the CT of your filament windings to a positive DC supply instead of ground. 50v or so should work fine. Even running AC heaters, if they are always more positive than the cathodes, you won't have emission from heater to cathode. This will reduce another place where hum enters the system.

 

 

Thanks for the great tips, I am going to go through all these posts and copy the pages with all this information. I can just make a posative source for the heaters by making something like another bias supply without the diode of course. If you PT has no CT on the 6.3Vac can you stil do this with floating a ground (w/100w res) to the 50v source?

 

I have my opening stage's, and the active EQ finished, I will get the Active midrange circuit, and the remainder of the preamp drawn as soon as I get the inductor.

 

Any comments on the Active EQ schematic?

[SomeoneYouKnew]

I have my opening stage's, and the active EQ finished, I will get the Active midrange circuit, and the remainder of the preamp drawn as soon as I get the inductor. Any comments on the Active EQ schematic?

Just one comment. The EQ pots are listed as linear in your drawing. I was almost certain log pots are used there.

[Casey4s]

Yes. I've seen a few designs that are done just like that with a pair of resistors to emulate a "center". I see no need to make another supply. You could just put a voltage divider on the B+ And you can kill two birds with one stone. The voltage divider can function as your bleeder resistor. Just one comment. The EQ pots are listed as linear in your drawing. I was almost certain log pots are used there.

 

 

Yes I am a bit confused on this issue. I researched Baxandall circuits and on HiFi they are log, but Ampeg uses a passive Baxandall with linear pots and some different cap values on the circuit. I am trying to Mimic the Ampeg tone stack but just make it active instead of the passive stacks used by everybody else.

 

Pots are easy to change if I need to, but I am going to start as drawn but I can tweak anything I have to.

[SomeoneYouKnew]

Casey, I just checked the ampegv4 site. They have factory drawings for my V4B as well as the V4/VT22 you used as a starting point for your design.

 

And I went back and looked at the Joe Piazza drawing in your OP.

 

They all show log pots for the Bass and Treble. Linear for the Midrange and Volume pots.

 

God only knows why they chose linear for the Volume. I can tell you from first-hand experience, these amps are touchy at low volume. Maybe they wanted the users to have finer control between LOUD and IN-YOUR-FACE-LOUD, or something?

 

But the B&T should be log and the Midrange should be linear.

[Casey4s]

LOL... I guess I'll change the schematic then. This is why I take my time in the design area.

 

The stage before the tone stack is a two triode Marshall style input section. Then the active B&T and the Mid section. So I am getting there, the output section is easy as is the reverb. The only troublesome portion has been the preamp.

 

This amps going to have elements from Ampeg, Marshall, and Fender thus far as well as a little help from the RCA manual.

 

This going to be a fun build (I hope)

[evelynz8735]

 

I have a V4B (bass amplifier). Very similar preamp. I really like the way this tone control system works. I'm not sure how the midrange control will act without the inductor. You should sim that, if you have the software. There is a LOT of gain available if you use a switch to add a bypass cap on the cathode of the second triode. Post PI MV does some nice things. Why do you prefer yours before the PI?

 

 

 

 

 

 

Thanks you for the post.

Hi guys, Im a newbie. Nice to join this forum.

 

Edit: Spam "sig" removed. ij

[SomeoneYouKnew]

Thanks you for the post. Hi guys, Im a newbie. Nice to join this forum. __________________ advertising link in fake signature

Say goodnight, spammer.

[Casey4s]

Here's today's sketch for a dual or switchable bias architecture. This is just a preliminary sketch.

 

With dual Bias and Dual Rectification, it should give this Amp 4 basic personalaties for a starting point.

 

 

 

 

 

Any comments or suggestions?

[SomeoneYouKnew]

Any comments or suggestions?

You need to make use of the upper left lug of the switch. That should be used to tie the 220k resistors to ground in the cathode bias mode. The grids need to be referenced to ground through the resistors. They can't be allowed to just float.

[Casey4s]

Yes I saw that almost as soon as I posted this so I did a new sketch.

 

[Casey4s]

SYK / SnorkleMonkey

 

OK, here's my next (actually first) section in volving four triodes. The first two inputs (at top) are into a basic Marshall style first stage. Input 3 goes into it's first triode with basic Fender values on the cathode, but I bridged the anodes and control grids at the tube socket, with K floating. When SW2 is thrown, it connects K to ground AND bridges the cathodes which then puts the 12AX7 into parallel mode increasing gain, providing BOOST.

 

I know I am going to need to tweak some values in the boost stage, I want it to sound agressive but not "over the top".

 

Is this even going to work or am I pissing into the wind here?

 

At C8 it goes directly into the EQ stage I posted earlier.

 

[SomeoneYouKnew]

You have a problem with C9, the coupling cap from V2. I suspect you'll want to connect that to the switched portion of the top input jack, same as you have C1.

[Casey4s]

You have a problem with C9, the coupling cap from V2. I suspect you'll want to connect that to the switched portion of the top input jack, same as you have C1.

 

OK, so you think I should connect V2 (C9) to the same place I have C1 connected to V1a between the anode and R4?

 

I am confused, and I believe you, but why is my method wrong?

 

 

Edit:

 

 

OK, are you suggesting the red path or the green path? (i forgot to include c9 in the green path btw)

 

 

 

OR something else?

[SomeoneYouKnew]

 

OK, so you think I should connect V2 (C9) to the same place I have C1 connected to V1a between the anode and R4?

No, I'm talking about where the other end of C1 is connected. The switched part of the top input jack.

 

With nothing plugged into the top jack, C1 and C9 will allow those first stages to be coupled to the second triode of V2. But if you plug something into the top jack, you don't want the coupling capacitors connected.

 

The way you have it: Best case, the caps will act like tone-cut circuits. Worst case, something else is connected to the bottom jack and the amplified signal is going back through the cable to whatever is connected to the top jack (like maybe a guitar pickup). bad juju.

 

 

 

EDIT:

Yeah, C9 has to be in the green path.

[Casey4s]

OK, I finally figured out what you were trying to tell me,LOL sometimes I get these brain farts and confuse myself.

 

THIS should do the trick...(me hopes)

 

[SomeoneYouKnew]

yep, looks fine.

 

 

Oh, as far as floating one cathode of the parallel triodes, I have no idea if that will be okay or cause some trouble. Never tried that.