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 Post subject: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 3:34 am 
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Starting a new threat about building the Princely Pauper. Flip got me going on this project.
Find the starting info here
viewtopic.php?f=12&t=273358&start=2000
Peter is being great help with some design changes.
The amp was designed to be built with economy in mind, but still HIFI.
A 15 watt per channel, stereo amp.
Please join us. All suggestions are very welcome.
Here is the PRINCE JOHN, thanks Flip.
/download/file.php?id=156067
download/file.php?id=155982
And here is the Prince John UL revision by Flip
/download/file.php?id=156536
download/file.php?id=160963
Dec 10-2016.
Flip is designing the preamp to go with the Prince John. It will be the Little Prince.
Here it is. I will update any changes as we go.
download/file.php?id=165323

download/file.php?id=163072
download/file.php?id=163998

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Last edited by john8750 on Jan Thu 05, 2017 3:27 am, edited 27 times in total.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 4:08 am 
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The 10-8-8K means it's 10 watt, 8 Ohm output, and has an 8K plate to plate impedance. I believe that's an 'old' Edcor designation and nowadays they make the output Ohms an 'option' to the basic part number rather than include it. Here's an old datasheet on it. https://www.edcorusa.com/Content/Manuals/XPP10-8-8K.pdf

Any 8k (with the appropriate speaker tap) transformer will work whether Edcor or not. Edcor is just the least expensive.

The schematic shows the Edcor XPP series, which is the least expensive and has a 70 Hz low end. The GXPP series is 40 Hz and the CXPP series is 20 Hz.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 4:16 am 
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This looks pretty straightforward to build. I still have plenty of amps to recap, and the cake pan amplifier that I started to build. I might get the tubes first, since they are pretty cheap. I will follow along on everyone else's progress for now.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 4:26 am 
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john8750 wrote:
I was wondering about tube cathode constant current. Yes, as we did on the 5902 and 6V6 amps.
What do you think about it Professor? Something sure made those amps sound superior.
I specifically avoided any solid state in the amp because it was supposed to be 'pure' (tube) but, yes, you could use a CCS for cathode bias. It's not needed, though, with 'real' OPTs (like the Edcors).

Even with the SPECO the intent was to avoid solid state and for idle 'current balance' I used a modified (adjustable) garter bias like this

Attachment:
Adj Garter Bias v7.jpg
Adj Garter Bias v7.jpg [ 67.31 KiB | Viewed 2389 times ]


Cross connecting the bias makes it close to self adjusting, if one tube conducts more the other is adjusted, with the pot being for fine trim. It's implemented as a side chain of resistors so a small (low power) trim pot could be used and I successfully used that mechanism on Top Cat.

For the 6HB6 amp I'd probably modify the circuit a bit because I was concerned with raising cathode voltage on Top Cat (due to not much B+ headroom). Technically a garter should double it (equal resistors on each side of the bias chain) and I edged it toward the low side for that reason. But the 6HB6 is already about half cathode bias so a normal garter would bring it back to almost the same bias as a 6BQ5.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 4:27 am 
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john8750 wrote:
...BTW- where can I get the tubes for your Pauper amp?
The power transformer you show for that amp has a single primary of 220 volts. What other can you suggest?
I have no problem using a couple diodes for the B+. So don't need the 5 volt winding.
I need to order asap. Along with the OT's. Cant start the amp for awhile though. Thanks again.
Rats. I didn't notice there wasn't a 120VAC option. Well, the next one up is the XPWR065. Same heater power, no rectifier, and 250 mA @ 500VCT. That's 'more than enough' so B+ may rise a bit.

Be aware that you may need to tweak things a little so build it in stages so you can debug each one. Power supply first, then the outputs and make sure idle current is correct, then the preamp. Once one channel is right the second should go without a hitch.

Tubes can be had from abcvacuumtubes.com. That's where I go to check prices and they're both dollars days right now.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 4:29 am 
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john8750 wrote:
Change order
Is this the correct OT for the Pauper?
http://www.edcorusa.com/cxpp10-8k
I might as well get the best. Very affordable and bigger is better.
Yes, that's the one.

Since everyone seems to be 'picky' :wink: I'll point out that's a 10 Watt OPT and the amp does 15 watt (and maybe a little more) so if you want 'bigger is better' you could move up to the CXPP25-8k (/23 if you want to play with UL taps).

I don't think it's necessary (obviously since I spec'd 10 Watt) since an OPT will pass much more power at the higher frequencies than the low and that 'extra' 5 Watt over 10 Watt would be nothing but transient peaks.

Btw, being cathode bias the amp won't do 15 Watt continuous (cathode voltage rise) so it's more a case of specmanship whether you use 10 Watt or 25 Watt (which is the nearest to 15 Watt in the CXPP). Now, they do have a 15 Watt in the GXPP but that's the 40 Hz job.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 5:27 am 
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OK, that's what it will be. Will decide about the CCS and UL changes later.
What does the % figure indicate by the volume pot? I should either omit the volume pot,
or install it on the chassis for a gain control from the preamp, coming later.
Thanks Flip.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 6:23 am 
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john8750 wrote:
OK, that's what it will be. Will decide about the CCS and UL changes later.
What does the % figure indicate by the volume pot? I should either omit the volume pot,
or install it on the chassis for a gain control from the preamp, coming later.
Thanks Flip.
The % figure on the volume pot is for SPICE to tell it the pot rotation (how much resistance is below and above the tap) and on my schematics it is usually (but not always) set to 1 Watt output (with the signal source set to "consumer line level" 316mVrms [which is 446.8mV peak]).

If you remove the pot you'll need to add a grid leak. 1Meg should be fine. The input cap sets the low end roll off so with a CXPP transformer you might want to increase it to .1uF with the 250K pot. With a 1 Meg grid leak it can be left at 47nF.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 6:56 am 
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If the current is 40ma per tube ... and you want to use an LM317 CCS for idle current bias, the formula for the resistor is 1.25/.04a = 31.25 ohms
So.. the standard closest resistor is 33ohms = 38ma

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 6:50 pm 
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Pbpix wrote:
If the current is 40ma per tube ... and you want to use an LM317 CCS for idle current bias, the formula for the resistor is 1.25/.04a = 31.25 ohms
So.. the standard closest resistor is 33ohms = 38ma



Thanks Peter. And thanks for you discovery of needing no voltage regulation, I have all the parts for the CCS,s already.
Should be a simple board to make.
Our open house is Oct 1st and 2nd. I will be busy till the 5th, so will just order some parts.
Why don't you build this with me, will be fun.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 10:22 pm 
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john8750 wrote:
Thanks Peter. .
Why don't you build this with me, will be fun.

The problem is, John:
... what would I actually do with it?
I'm already loaded up with three fantastic amps. They completely fill up my living-room stereo-cabinet now as it is!
And I can only listen to one at a time.

As it is, I paid over $575 for the ASL 30 watt amp and I never use it because I love the 6v6 amp.... and it's MY creation. So the ASL sits there idle. What a waste. No?

So I'm already conflicted... lol

Look inside my stereo cabinet. I'm already in "amplifier overload":
1.) The sweet sounding and lovely to look at 6v6/6AQ5 amp
2.) The 45 pound BIG GIANT 30 watt EL34 amp ASL AQ1003-DT
and
3.) My Original lovely beautiful sounding 5902 amp

Attachment:
3amps.jpg
3amps.jpg [ 125.9 KiB | Viewed 2297 times ]

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Last edited by Pbpix on Sep Tue 20, 2016 2:49 am, edited 1 time in total.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 10:48 pm 
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I hear that Peter. I have the same situation. But wanted to just build and show the all tube amp, and preamp.
I don't expect it to sound better than my 6V6 as it is. Just to sit on a shelf for show.
That's why I wanted the Pauper. I considered other amps, like the ones you suggested.
But decided on this one because Flip knows all about it, and you could work on some
details I would like to change. I hope you are on board.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Mon 19, 2016 11:06 pm 
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john8750 wrote:
I hear that Peter. I have the same situation. But wanted to just build and show the all tube amp, and preamp.
I don't expect it to sound better than my 6V6 as it is. Just to sit on a shelf for show.
That's why I wanted the Pauper. I considered other amps, like the ones you suggested.
But decided on this one because Flip knows all about it, and you could work on some
details I would like to change. I hope you are on board.

I'll be following along John.. but short or ordering all those parts and building it too... what else can I do?

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 12:59 am 
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Pbpix wrote:
john8750 wrote:
I hear that Peter. I have the same situation. But wanted to just build and show the all tube amp, and preamp.
I don't expect it to sound better than my 6V6 as it is. Just to sit on a shelf for show.
That's why I wanted the Pauper. I considered other amps, like the ones you suggested.
But decided on this one because Flip knows all about it, and you could work on some
details I would like to change. I hope you are on board.

I'll be following along John.. but short or ordering all those parts and building it too... what else can I do?



You are doing fine. I appreciate your help always. Together, we can help Flip prove this amp to be a fun and practical project.
Just something to do while we get old. Like all the cool info you find for me to check out. Thanks to you guys, the basic
power amp schematic isn't so tough to follow now. I guess learning is most of the fun. 8)

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 4:44 am 
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Pbpix wrote:
john8750 wrote:
Thanks Peter. .
Why don't you build this with me, will be fun.

The problem is, John:
... what would I actually do with it?
I'm already loaded up with three fantastic amps...
I know what you mean. I have 6 tube amps, not counting guitar amps and the two I made for family. Oops, I forgot the signal tracer that I turned into a Bluetooth cellphone amp. That's one reason why I started using 1/4" phone jacks for the speaker connections, or else I'd be hip deep in speaker cabs too. :lol:

I use a couple for PC speakers but that still leaves more than I 'need'. They're just fun to build but it's gotten to where there has to be something 'new', 'interesting', or 'challenging' about them.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 5:54 am 
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Flip:
I was looking over that schematic tonight with John and was wondering why you selected 19db of NFB?

What is that value determined by?

I thought maybe more or less FB is determined by if the OT is poor, more is needed and less if it's a good one?

...and what does "Av125" mean?

I don't understand the input signal level of +/-450mv.

Does it require that high of a signal level for normal input? Or is that a max input test level to get max output?

Will an Mp3 output be sufficient as input signal?

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 8:48 am 
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Pbpix wrote:
Flip:
I was looking over that schematic tonight with John and was wondering why you selected 19db of NFB?

What is that value determined by?

I thought maybe more or less FB is determined by if the OT is poor, more is needed and less if it's a good one?

...and what does "Av125" mean?

I don't understand the input signal level of +/-450mv.

Does it require that high of a signal level for normal input? Or is that a max input test level to get max output?

Will an Mp3 output be sufficient as input signal?
Negative Feedback reduces distortion and improves the amp's damping factor. In theory the more the better but phase shift at high frequencies limit how much can be applied before it turns it to positive feedback and the amp becomes unstable. 20 dB is a relatively safe number (on the Princely Pauper 19 dB is the estimate as a result of standard values). I used 20 dB on Stealth AX with a line transformer (and later Ebay bought Harman Kardon OPTs). The famous Williamson design was up to 30 dB (with their 'super duper' OPT design).

The 'quality' of the OPT has little to do with it except for limiting how much can be applied before high end phase shift turns it into positive feedback and the amp becomes unstable. All NFB amps have that problem sooner or later and that's what the little cap across the feedback resistor handles. If the OPT is lousy enough the frequency response must be limited to keep it stable but, as noted, I've not had a problem with line transformers and I certainly don't anticipate there'll be any with the Edcors.

The amount of feedback subtracts from the overall gain and 20 dB was as much as I could get and still have respectable sensitivity without adding more tubes and further complicating the amp. It was, after all, intended to be a simple and inexpensive 'Hi-Fi' design. You could lower the feedback to get more sensitivity but distortion will increase, and damping factor decrease, by the same amount.

Av125 is the estimated preamp gain and mainly for my use when working on the design.

The 450 mV is peak to peak and corresponds to consumer line level of 316mV (rms) which, in turn, corresponds to nominal program level (not max or peak). I use that on all my 10 to 20 Watt amps to equate to 1 Watt output (less on the smaller ones), with the rest of the power reserved for transient peaks. It's also what the distortion figure is based on. I then look to the 'vol' pot rotation to see if it's too much or too little. 25% is about right and means that roughly 80 mV on the grid produces 1 Watt. 316mV(rms) on the grid (or full pot rotation) produces the full output of 15 Watt, which is the "sensitivity." By comparison, the Harmon Kardon Citation V has 1.2V(rms) sensitivity and takes almost 4 times the input voltage as Princely Pauper. The comparable Dynaco ST-35 takes 1V(rms).

MP3 players and cellphones have less than normal line level but it should still be sufficient to drive the amp to full volume (it is on my Top Cat amp, which has the same sensitivity). With those low levels you won't be able to overdrive it into massive clipping though but, then, that's not Hi-Fi.


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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 12:46 pm 
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A side note on negative feedback...

How much can be used depends on the open-loop frequency response---- more precisely, the frequency and phase response. Any component that affects these parameters will affect how much feedback can be used.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 5:58 pm 
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Flipperhome wrote:
Negative Feedback reduces distortion and improves the amp's damping factor. In theory the more the better .....

Why is more better?
Intuitively it just kinda seems a bit illogical in a way, because if we apply a 100mv of neg FB to a 100mv input signal... wouldn't that cancel completely?

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Last edited by Pbpix on Sep Tue 20, 2016 10:36 pm, edited 1 time in total.

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 Post subject: Re: PRINCELY PAUPER
PostPosted: Sep Tue 20, 2016 6:42 pm 
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Flipperhome wrote:
Pbpix wrote:
john8750 wrote:
Thanks Peter. .
Why don't you build this with me, will be fun.

The problem is, John:
... what would I actually do with it?
I'm already loaded up with three fantastic amps...
I know what you mean. I have 6 tube amps, not counting guitar amps and the two I made for family. Oops, I forgot the signal tracer that I turned into a Bluetooth cellphone amp. That's one reason why I started using 1/4" phone jacks for the speaker connections, or else I'd be hip deep in speaker cabs too. :lol:

I use a couple for PC speakers but that still leaves more than I 'need'. They're just fun to build but it's gotten to where there has to be something 'new', 'interesting', or 'challenging' about them.



How about an amp in every room, or a contest to display one amp every month. If vibrators are still available, one in the car.
Of course I'm just being funny. But I am a funny kind of guy.

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