Topic: Surplus amps

[rascal101]

I'm reading about capacitors today. How convenient hehehe

How do you determine the value you need?

TIA

It is determined by

1.  How much hold-up time you require - meaning to say when you turn-off the appliance, how long before the PSU can supply regulated voltage to the circuits

2. How much current is required by the circuits (I = C x dV/dt)

[bumblebee]

Is hold-up time critical? For surplus amps and other applications

[JojoD818]

C = (Ilc/dV) x k x 1,000

C = capacitance in uF
Ilc = load current
dV = peak-to-peak ripple voltage
k = is "6" for 120Hz or "7" for 100Hz (use "6" since Philippines has 60Hz line frequency)


cheers

[bumblebee]

Thanks guys. The "ripple" keyword did it for me

[rascal101]

Is hold-up time critical? For surplus amps and other applications

To a certain extent ...

[aHobbit]

Most if not all the bulk e-caps exceed their computed life which is typicall around 5 years assuming 24/7.

... but ... if not used 24/7?      ... unless I will assume the previous owner of my gear listens with an equivalent of 5 years 24/7    ... notwithstanding, the gear is supposed to be high end model with quality (long life?) parts  ...


Sir Tony,
if one has to go recapped ... mga magkano abuting typically ?    ...

[ATJr.]

When do you use it? How do you determine the value you need?

when voltage levels of the succeeding stage prevents direct coupling, then you use them, or when you are uncertein of what dc voltage your input will see, you better use them.

when more ac gain is required, then you bypass emitter resistors with caps, when you want to roll-off certein frequencies and shape the frequency response of your amp, then you use them.

on dc rectifiers, capacitors are a must, lowers the ripple voltage to almost nil...

the values are determined by certein considerations as voltage levels, ripple requirement and frequency cornering..

and i end with a note, the best coupling capacitor is no capacitor....

[ATJr.]

if one has to go recapped ... mga magkano abuting typically ?

be prepared to spend as much as the acquisition cost..

[squidball]

Mga sirs where would be the best place to recapp your surplus amps? Any suggestions? 

[bumblebee]

What's the difference between recapping and replacing the caps?

[JojoD818]

What's the difference between recapping and replacing the caps?

good question bro. I think it's the same thing. 

maybe recapping is reforming?   

[seanramos]

Hi! Iam seanramos, bago lang ako d2 and gus2 ko sanang bumili din ng Amp from pier. Tanong ko lang okay ba ang AU-D607, AU-D607F Extra or AU-D507X ng sansui and which is better sa tatlo kasi sabi ng iba this model was made in the early 80's? T.Y

[ATJr.]

author=bumblebee link=topic=15332.msg618488#msg618488 date=1157761563]
What's the difference between recapping and replacing the caps?

 i mean replacing caps along the signal route...includes bypass also.

[bumblebee]

good question bro. I think it's the same thing. 

maybe recapping is reforming?   

Akala ko kc iba. Tinanong kc ni aHobbit yung price Reforming nga yung naiisip ko.

[JojoD818]

Akala ko kc iba. Tinanong kc ni aHobbit yung price Reforming nga yung naiisip ko.

for me it's a valid question talaga bro. imagine the so many terms we are using regarding caps, this way we can set the terminologies straight. 

 

[ATJr.]

What's the highest microfarad value for a filter cap available locally and how much? 

last time i checked with DEECO, they has 33,000ufd/63volts selling for 650 a can, and 22,000ufd/100v selling for 970...but you can also get those computer grade caps from the Raon sidewalks for 250 a piece, but you will have to "reform" them before using.

[ATJr.]

Is hold-up time critical? For surplus amps and other applications

asfaik, they have no relevance to amps in genral, they are relevant to switching psu's as the main filter caps ought to have a certein hold-up time to maintain their charge under load, or hold up time for the output voltage to stabilise before a "power good signal" is asserted.

[ATJr.]

That's the common observation.  Both by professionals and amatuers,  Toroids are difficult to wind.  And that is what makes it more expensive, not the core material.   I really suggest people try it one of these days to see how "easy" it is even with just one layer over a doughnut ferrite core.     But there are actually some techniques I heard that make it easy,  just can't recall those. 

yup, it is really hard if you do it by hand, but nowadays, there are "machines" that can wind them quickly and in a mass production type runs just like EI's.....mass production lowers the costs, so that the torroids being more expensive than EI's can easily be a myth also...

here's what the folks over at diyaudio are saying about this topic.:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=1130

[bumblebee]

Here's what I found.

http://leeh.ee.tut.fi/transformer/dirmap.htm

[rascal101]

when voltage levels of the succeeding stage prevents direct coupling, then you use them, or when you are uncertein of what dc voltage your input will see, you better use them.

when more ac gain is required, then you bypass emitter resistors with caps, when you want to roll-off certein frequencies and shape the frequency response of your amp, then you use them.

on dc rectifiers, capacitors are a must, lowers the ripple voltage to almost nil...

the values are determined by certein considerations as voltage levels, ripple requirement and frequency cornering..

and i end with a note, the best coupling capacitor is no capacitor....

If you have very little (almost nil) ripple voltage, you will have very little input current going to to main circuits. This is because it is only when the input ac voltage is higher than your bulk voltage is the rectifiers conducting. With very little input current, you will have lower efficiency. So their is a trade-off between ripple voltage and efficiency.

[ATJr.]

If you have very little (almost nil) ripple voltage, you will have very little input current going to to main circuits. This is because it is only when the input ac voltage is higher than your bulk voltage is the rectifiers conducting. With very little input current, you will have lower efficiency. So their is a trade-off between ripple voltage and efficiency.

this is beyond my comprehension, hmmm wonder what's on your mind

[bumblebee]

Tama ba ito? Zero ripple = no need to regulate?

[JojoD818]

this is beyond my comprehension, hmmm wonder what's on your mind

naku, efficiency na naman 

j/k

Tama ba ito? Zero ripple = no need to regulate?

if your load constantly changes, then there would still be ripple.

[ATJr.]

Tama ba ito? Zero ripple = no need to regulate?

no, there are other reasons why you want to regulate, and psu ripple is just one of them. tubes and transistors will most likely change their operating points with a change in supply voltage, is this bad? not nescessarily, but a change in operating point can contribute to distortions otherwise avoided when rails are held constant.

[rascal101]

Tama ba ito? Zero ripple = no need to regulate?

Bulk voltage ripple is normal, this is why you have post-regulators to minimize ripple voltage effects.

[sebman]

mga surplus gurus... pa-comment naman sa sansui a70.. oks ba tong amp na to? maraming salamat.. 

[rnb_zounds]

Greetings,

I found this in a surplus shop. Bought it for 1.5k after making some tawad from 1.8k.

SONY TA-5650 VFET

Here :



Not, the actual pics but exactly the same even inside.



Power up lang no testing at 100V. I knew I was taking a big risk but since I was not able to go to Nadb for his cheap stuff.      Eto nalang kinursunada ko. Power button lights up green. Knobs were easy to remove so I was able to clean the face very well. A few edge scratches and bumps at yung top cover meron dent yung isang grille element but otherwise ok naman. Cleaned the insides - well mosty the transformer and the power board with twin fuses was all that needed the dusting. No wood sidings as some units had. Good thing there was no scratchy sound in any of the knob controls or switches.

Used the amp over the weekend and no problems naman and in fact malakas as I never had to go over 10 o'clock sa volume as it was loud enough na for me.  Checked DC offset voltages and came out with the following: Left Channel : 24-28 mV. Right Channel: 7-9mV.     

Read somewhere that these amp should run hot. However this one ran pretty cool naman even touching its twin "chimneys" inside. Well, warm yung fins ng heat sink and I suppose that's normal.

Tested the AUX inputs using my CD player and the tape inputs I also tested and they were OK. Next weekend try ko yung phono stage. Cheerio.

SPECS. Accoring to Vintage Knob


POWER:                        2x 70W (IHF, 4Ohm)
                           2x 80W (IHF, 8Ohm)
             
Continuous RMS:         2x 50W (20...20kHz, 8Ohm)
 
Frequency response:    5Hz...40kHz
Bandwidth:                   2Hz...100kHz (-2dB) 
THD:                              0.1% (rated power)
                                     0.08% (1W)


Damping factor:         50 (8 Ohm/1.0kHz)
S/N ratio:                  110dB
Residual noise:           0.02µW

S/N ratio:              70db (phono)
                             90db (tape, aux)
 
RIAA deviation:         -0.2db

Inputs:                   2x Phono (2,5mV/50kOhm)
                              3x Aux
                              1x Tuner
                             2x Tape (150mV/250kOhm)


Outputs:                 2x loudspeakers pairs (4Ohm min.)
                         2x Tape (150mV/4,7Ohm)
                         1x DIN (17mV/42kOhm)
                         PRE OUT (150mV/47kOhm)
                         headphones


Bass controls:           ±10dB@100Hz or 50Hz
                  (turnovers: 500Hz or 250Hz)   

Treble controls:         ±10dB@10kHz (turnover: 2,5kHz)
                     ±6.5dB@ 20kHz (turnovers: 5kHz) 


Low filter:               12dB/oct. above 30Hz
High filter:              12dB/oct. below 9kHz
Loudness:                +10dB@50Hz, +3dB@10kHz

Componentry:   10 V-FETs
                           8 FETs
                          42 transistors
                          31 diodes

PC:                      440 Watts
Dimensions:        430 x 168 x 323 mm
Weight:               12.5 kG

[rascal101]

Wow! Ganda niyan Sir Ryan.

Three wks ago got myself an Onkyo M-506 power amp at the Pier.

[rnb_zounds]

Sirs,

Meron nga pala akong nakita na Sansui AU-555. Pina buksan ko para tignan, malinis naman. Kaya lang pag power on, after a while, me pumutok malapit sa mga power caps. Wala namang usok, at parang buo pa naman yung mga capacitor, pinatay, tapos pag on ulit, parang nag hu hum (walang speakers na naka kabit pero yung body ng amp eh nag reresonate at parang nag huhum ng mababa - baho ika nga) , tapos pinatay, pag on ulit di na umilaw power lamp dahil pag tingin namin bumigay na pala yung fuse. Tried substitute, ganon din. What could possibly be wrong with the unit?







Sayang, malinis pa naman yung labas at kahit yung loob. Although hindi naman ito high end, ang alam ko kasi yung 3 digits na series na ito lumabas about my time din kaya parang gusto kong buhayin. Sigurado naman pwede ko makuha ito ng malamang less than 500 o baka libre na. Kaya lang baka super gastos naman pag inayos ko. One good thing though, me kasama nang schematics, naka tape yung envelope sa ilalim ng amp! hehehe ok din yung dating me ari nito.

[av_phile1]

Humming even without speakers connected?   Have never encountered this though I've read about transformers making humming noise due to their core construction failure or what they call lamination rattle that literally causes the transformer core to vibrate.  Yung umusok could be the lamination burning, just guessing though.  A short may have developed in the windings to deliver voltage or current outside the rail fuse tolerance.  Maybe changing the power transformer is all that is needed.