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Leonardo Capossio <capossio.leonardo@gmail.com>: Nov 24 01:37PM -0800 El jueves, 15 de octubre de 2015, 18:11:29 (UTC-3), Leonardo Capossio escribió: > Well, in the end the problem were those resistors, now it works like it should. The only problem is that at high volumes the amp turns the sound off after a while, I guess because of thermal shutdown of the PT100 on the power dissipator. But this can be solved by cleaning and re-applying thermal paste, and in extreme situation adding a cooler.   Unfortunately after re-applying thermal paste on the heatsink and the power transistors, and adding a cooler on the far side (not exactly by the heatsink) to blow hot air out of the amp head, the amp still behaves the same. It turns off the audio (LED and cooler are still working) after a couple of minutes of playing.   Anyone can point out to what might be the problem ?

M Philbrook <jamie_ka1lpa@charter.net>: Nov 24 05:59PM -0500 In article <b9e7a5a8-3dd2-4875-9b1e-ddf77935405e@googlegroups.com>, capossio.leonardo@gmail.com says... > > Well, in the end the problem were those resistors, now it works like it should. The only problem is that at high volumes the amp turns the sound off after a while, I guess because of thermal shutdown of the PT100 on the power dissipator. But this can be solved by cleaning and re-applying thermal paste, and in extreme situation adding a cooler.   > Unfortunately after re-applying thermal paste on the heatsink and the power transistors, and adding a cooler on the far side (not exactly by the heatsink) to blow hot air out of the amp head, the amp still behaves the same. It turns off the audio (LED and cooler are still working) after a couple of minutes of playing.   > Anyone can point out to what might be the problem ?   Does the outputs on the sink actually feel like they are getting that hot? DO you have a IR tool to meaure it? Most likely not..   If you feel the unit isn't that hot and should be able to maintain output at that temp? then maybe the PT resistor has degraded. They do drift a little over time. You could try checking all of the R's in that ciccuit to make sure they are on track.   Looking at the schematic it looks like you have at least 2 R's that could be suspect. That would be in the lower left about 1/2 the way over.   If you have some kind of component cooler you can spray the PT while its operating and see if it extends the on time. Or blow on it using a straw.   Jamie

dansabrservices@yahoo.com: Nov 24 03:10PM -0800 Put a scope on the outputs and look for very high frequency harmonics. Perhaps the system is working too hard on things you can not hear.   Dan

makolber@yahoo.com: Nov 25 07:26AM -0800 > Put a scope on the outputs and look for very high frequency harmonics. Perhaps the system is working too hard on things you can not hear.   > Dan   good point     logical seteps is it actually getting hot? if not, the thermal shutdown system could be faulty   if it is getting hot you need to figure out why.... there could be an ultrasonic oscilation in the amp the quiescent bias current could be too high in the amp there could be some kind of short or overload at the output of the amp, bad speaker?   have fun , fixing stuff is a great way to learn   Mark

Leonardo Capossio <capossio.leonardo@gmail.com>: Nov 25 08:13AM -0800 > there could be some kind of short or overload at the output of the amp, bad speaker?   > have fun , fixing stuff is a great way to learn   > Mark   Don't have a scope, best I can do is a DMM.   Just to clariphy, the audio from the amp gets cut abruptly. Everything is working like a charm, the sound isn't fading away or anything, and the suddenly it stops outputting audio. Everything else seems to be working.   In this case, the only thermally dependent element I see is the PTC100. The circuit surrounding the PT100 seems to be compensating the bias current of the power amp, though I do not understand it fully, if anyone can point to a source that explains how this circuit work it would be great. To me it seems very strange that it abruptly cuts out the sound.

thekmanrocks@gmail.com: Nov 24 02:11PM -0800 N_Cook:   See that black thing on the edge of the widest part of the megaphone?   https://jet.com/product/pdp/bfec71f641d1435e9a4ef536ff6a90b7?jcmp=pla:ggl:cwin_electronics_a3:audio_bullhorns_a3_other:na:na:na:na:na:2&code=PLA15&k_clickid=67872188-ced8-47d1-9bdb-963ffdb2cc68&gclid=CjwKEAiAstCyBRDiqu75hvnX82kSJACgYI_QrQ4JhTcp5WnemAgaDGlXq_ifOupNfSHoNJUHvVj3aRoCXifw_wcB     That is what I'm referring to.

Clifford Heath <no.spam@please.net>: Nov 25 12:02PM +1100 > was provided showing the propagation of sound from > megaphones both with and without this rubber ring on the > edge of the flared horn. Cannot seem to find it nowadays.   I suspect it has a major effect in damping the high-Q mechanical resonances of the cone, and so improving the sound quality.

jurb6006@gmail.com: Nov 24 07:41PM -0800 I am sure it does affect the sound, but in a very small way. If you did it with alot large horn and an audiophile driver in it, I am sure the "golden ear" crowd could tell the difference.   The way to test it would be a short burst tone and a scope to read the ringing. Or perhaps a square wave and you watch the leading edges. Or course it might only be difference of 8 cycles versus ten cycles.

adrian@poppyrecords.invalid.invalid (Adrian Tuddenham): Nov 25 09:42AM > The way to test it would be a short burst tone and a scope to read the > ringing. Or perhaps a square wave and you watch the leading edges. Or > course it might only be difference of 8 cycles versus ten cycles.   It would reduce ringing in the metal or fibreglass 'bell' of the horn. Just tap the horn and listen to the 'clang' sound with and without the ring.     -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk

"pfjw@aol.com" <pfjw@aol.com>: Nov 24 01:32PM -0800 On Friday, November 20, 2015 at 3:55:22 PM UTC-5, Madness wrote: > style as lamps like the #44/47. But would anyone know if these lamps can > be connected directly to 120 volts? Or do they need a resistor, @ if so, > what value?   Mpfffff....   This lamp was used by Zenith and more than a few other manufacturers in the 1950s/1960s as an indicator lamp (on/off) at about the time that radio manufacturers started to become concerned about user-servicing and hot-chassis radios - something that never really bothered them in the past. The worked on the theory that a neon lamp was far less likely to burn out than the old standby #44 or #47, so that loose fingers were less likely to get nipped. ASIDE: Audio devices held on to incandescent lamps (With specific reference to the 47) well into the 80s, before shifting - very slowly - to LEDs or Fluorescent lamps. But, they had transformers on board to isolate the chassis.   It is designed to operate at ~120V AC. It _CAN_ operate at ~120V DC, but only one post will light. It will trip (glow) at about 90V +/-.   Unless there is a voltage dropper in the circuit, it will fail quickly at 220 or 240 V - that is voltages outside of Japan and the Americas. As supplied, it has a 100K resistor in series with the lamp. For conversion to 220V, I have heard values of up to an *additional* 220K in series. Try there and work back if you wish to operate at 220V.   As about 2/3 of my hobby time is dedicated to vintage radios, I am quite familiar with, and keep a bunch of these lamps in my spares-box.   Peter Wieck Melrose Park, PA

Bennett <bjprice@cal.berkeley.edu>: Nov 24 11:56AM -0800 There's a possibility that the remote isn't the issue. The door might simply be stuck and repeated button pushes finally 'pry' it loose.     On 11/18/2015 8:44 PM, isw wrote:

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