Hitachi HMA-8500 MKII FET Recap advice
I'm starting restoration project of lovely sounding Hitachi HMA-8500 MKII FET power amp. Think it'f from circa 1984
Plan is to replace speaker relays, speaker terminals an least all electrolytic caps. There has been couple things that i'm not sure and would greatly appreciate advice. Attached is schema and component list
1. Main DC caps are 8pcs 6800uF 63V 30x80mm. Is it safe to use little bigger ones, like 10 000uF?
2. What are the caps on signal path that should need special attention. For example to use something like Wima MKS to replace elko's?
3. There is types of capasitor on part list like Ceramic discal, Film fe, Mylar film. How does these things age, should i replace?
4. What about other components that needs attention?
Kalle
I'm starting restoration project of lovely sounding Hitachi HMA-8500 MKII FET power amp. Think it'f from circa 1984
Plan is to replace speaker relays, speaker terminals an least all electrolytic caps. There has been couple things that i'm not sure and would greatly appreciate advice. Attached is schema and component list
1. Main DC caps are 8pcs 6800uF 63V 30x80mm. Is it safe to use little bigger ones, like 10 000uF?
2. What are the caps on signal path that should need special attention. For example to use something like Wima MKS to replace elko's?
3. There is types of capasitor on part list like Ceramic discal, Film fe, Mylar film. How does these things age, should i replace?
4. What about other components that needs attention?
Kalle
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I think you made a point of mentioning that it was great sounding, with that, I would just stick to replacing the electrolytic parts and leaving the film and ceramic parts alone.
10,000uf won’t hurt anything either...
Some of those old relays can be challenging to find, I hope they are the more common ones.
Still a good idea to make yourself a lightbulb tester for starting up after any work, if you don’t have that already.
10,000uf won’t hurt anything either...
Some of those old relays can be challenging to find, I hope they are the more common ones.
Still a good idea to make yourself a lightbulb tester for starting up after any work, if you don’t have that already.
I was thinking specially the C716 that is bipolar elko 10uF 16V that seems to be on signal path. Any good ones to put there.
For relays i did order these
Hitachi HMA-7500II HMA-8500II MKII Lautsprecher Relais / Speaker Relay Set | eBay
Pap-audio-parts realay with adapter pcb. Price is quite steep, but yes, original type of relays are hard to find.
About DC-cap, thing that worries with 10000uF caps is higher inrush current when powered up. Don't know if other components can handle it.
For relays i did order these
Hitachi HMA-7500II HMA-8500II MKII Lautsprecher Relais / Speaker Relay Set | eBay
Pap-audio-parts realay with adapter pcb. Price is quite steep, but yes, original type of relays are hard to find.
About DC-cap, thing that worries with 10000uF caps is higher inrush current when powered up. Don't know if other components can handle it.
Ok, what is effect of high dI/dt here? Maybe damaging of rectifying diodes or voltage ripple due spiking? What kind of wattage these resistors should be?
C861 is "West Germany only" component. Seems like this one doesn't have it. Maybe should add it with 20R and .01uF
C859, C860 could be some kind of filters related to transformer inductance and diode switching?
Would also like to get some comments about pre stage capacitors. I would like to believe that there is room for improvement with modern components
Only works on German electricity!
Must be why the BMWs 4wd isn’t that great here, only works in German snow...
But really, some r in there, value not critical, would be better.
As far as C859,860 goes, all they do is couple the ac to the dc side at a high frequency, not something that any other amp I have seen, nor any additional line or noise filtering would have either!
Must be why the BMWs 4wd isn’t that great here, only works in German snow...
But really, some r in there, value not critical, would be better.
As far as C859,860 goes, all they do is couple the ac to the dc side at a high frequency, not something that any other amp I have seen, nor any additional line or noise filtering would have either!
Hi guys, I have one of these amps, but it seems to have a problem, when powered on, the light on the display at the 4/8 ohm switch starts to blink rapidly. Do you guys know what causes this? There are no fuses blown as the unit fires up as it should, background light lights up only the relay does not switch.
Also, if you switch the other knob "BLT" next to the 4/8 Ohm switch, then that red light starts to flicker. Is it a protection mode? And if so how do I resolve this?
Also, if you switch the other knob "BLT" next to the 4/8 Ohm switch, then that red light starts to flicker. Is it a protection mode? And if so how do I resolve this?
Hey Dan75 did you ever figure out what was wrong? Mine just started doing the same.
it is a fairly complex amp and the possible causes are multiple.
Apart from a model specialist, or if you are a real technician in electronic troubleshooting, it is unlikely that we can help you remotely.
what I know of this amp is that its power supply is very strange and that in general, you should not put your hands in it without knowing exactly what you are doing.
I don't think it helps you, but if it can get you to find a specialist to check it, it may save you more damage.
if however you know what you are doing, start by checking the biases on each side, at start-up then when they are hot.
Apart from a model specialist, or if you are a real technician in electronic troubleshooting, it is unlikely that we can help you remotely.
what I know of this amp is that its power supply is very strange and that in general, you should not put your hands in it without knowing exactly what you are doing.
I don't think it helps you, but if it can get you to find a specialist to check it, it may save you more damage.
if however you know what you are doing, start by checking the biases on each side, at start-up then when they are hot.
Hi guys,
I just today buyed one Hitachi HMA 8500 mkII but my happiness didn't last long unfortunately, the vu meter on the right side went off, have no idea what's happened, on the left side it's still working normal as everything else. Any ideas what can be there for a problem? Is this difficult to fix?
Regards
I just today buyed one Hitachi HMA 8500 mkII but my happiness didn't last long unfortunately, the vu meter on the right side went off, have no idea what's happened, on the left side it's still working normal as everything else. Any ideas what can be there for a problem? Is this difficult to fix?
Regards