• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Choosing a tube amplifier to build, HELP needed

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#181
rongon said:
In the schematic in post 174, what is the purpose of D1 and D2?

D3 in the center tap of the 70VCT winding looks like it floats the center tap below ground. But then the anodes of D4 and the reservoir and the positive ends of filter caps C8 and C9 are grounded to 0 volts. Problem? Should those be 'grounded' to the anode end of diode D3? (I've never seen this done before, and I'm not understanding exactly how it would work...)

The schematic doesn't show it, but you'll want to create a center tap out of 47R 1W resistors for the 6.3V AC winding (for the heaters). You may also want to bypass that winding to ground with two 0.01uF polypropylene film caps (to bypass RF). Maybe cheap ceramic disc caps of the same value would do just as well?
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Click to expand...


Ron,

D1 and D2 are "check valves" that are part of the decoupling networks. Volts are at a premium here and the necessary small value resistors alone will not do an adequate job. The diodes ensure energy enters the decoupling caps., but does not leave.

The 2 rails from a single CT winding idea was publicized by Pete Millett. Twin Schottky D4 forms the connection to ground for both rails. The "tall" rail is a full wave bridge across the entire CT winding. The "short" rail is FWCT rectified. While Schottky D3 theoretically could be omitted, its presence is insurance against several problems.

All,

I've been putting off reviewing the latest PSU schematic. Some minor changes are forthcoming.
 
#182
I just can't wait for it! 🙂 I know, I need to be patient! I just hope I'll find every part I need.

I am thinking about changing the O/P Transformers... Is changing Edcor CXPP60-MS-6.6K to a similar transformer which are more available in Hungary would be as good as Edcor? I don't know if there is any shops in Europe for really good trannies.
Any opinions? 🙂
 
#184
Obisix said:
Maybe this One would work aswell Eli? Rongon?
Ogonowski.eu - profesjonalne transformatry do wzmacniaczy lampowych

I Just realized it is at the same price as I would order the Edcors. I Just try to cut down the prices as much as I can 😀
Click to expand...

It's kind of difficult to say if one is 'better' than the other. The frequency response specs are identical (20Hz - 20kHz -1dB). The Ogonowski transformer's primary inductance is listed at 47 H. That's OK, I think. The Edcor's primary L is unknown.

Hopefully someone with more transformer knowledge will see something that makes a clear difference.

- RG
 
#187
Sebastian,

A question remains about the full power bandwidth of the Hammond "iron". 🙁 If the Edcor product is close in price, that's (IMO) the way to go. OTOH, a big price difference makes Hammond the winner, in your budget constrained situation.

Please look carefully at Hammond's wiring diagram. Notice the dots on the blue (primary) and black (secondary) leads. Those dots are phasing indicators. The transformer must not invert phase. Therefore, the leg associated with the LTP's inverting leg, connects to the brown and brown/yellow primary leads.
 
#188
Okay, got it.
It would cost me 100$ -150$ (depending on later customs when coking unto Hungary) less, I really don't want to throw out money on the window, this is why I suggested several European transformers.
What do YOU recommend Eli? If you say Edcor I'll get it, since I trust you enough to count on your choice, and I'll pay a bit more 🙂
 
#189
Sebastian,

"Money talks and bull$hit walks." Use the Hammond O/P "iron". We'll make sure nothing bad happens by moving the "corner" frequency of the I/P high pass pole upwards. Change value of the grid to ground resistor associated with the inverting triode of the LTP to 100 Kohms. That value combines with the 0.068 μF. cap. to yield a F3 of 23.4 Hz.

Very, very, little musical info. can be found in human hearing's 1st octave. The lowest note a "normal" double bass makes is 41 Hz. 😉
 
#191
I am not impatient, but I really have to orer the Irons Eli! If you would mind telling me if I can order the choke/O/P Irons, that'd be great! 🙂 I am really excited about that review of the PSU!

Okay, recalculated 🙂 🙂 🙂
Hungarian Forint (our currency) is getting weaker and weaker and now edcor became solid unobtanium here, as shipping and the irons price would go over 400 USD...

So it would be lovely if we could revert to those Hammond Irons, since only european transformers became my only choice...

*.sigh.*

Sorry for being so unstable, my finances are fluctuating like crazy 🙂
 
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#193
I hope you meant it like so! 🙂
 

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