I have a old fiebird 500.Poid $100.00 for it.Works good pep about 375 with 3 watt dead key.When amp keyed it keys 150 when slumps off to 125 and slowly comes back.Tubes are not top shelf.Is it a tube issue or a capasitor issue.Trying to educate myself.I respect electricity and have proper toys to check that it is dead.
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firebird 500 Power sagges then comes back?
- Thread starter Droopy Drawrs
- Start date
It's a little like "my car just stutters if I try to push it past 45 mph". Might be a clogged fuel filter. Might be something ruinously expensive gone bad.
First thing to find out is the position of the Plate Tune knob when it's on the peak. If this changes when the power drops from where it peaked showing full power, this points to the output circuit.
The power supply can do this, but one or more of the HV filter capacitors will typically be getting hot if so. Good way to die, touching a high-voltage capacitor before it's safely discharged.
Tube can do this, too. Tubes that got pushed way too hard can have separated spot welds, allowing metal parts to change shape as they heat up.
Or you may have all three of those problems and another one I haven't thought of to boot.
73
First thing to find out is the position of the Plate Tune knob when it's on the peak. If this changes when the power drops from where it peaked showing full power, this points to the output circuit.
The power supply can do this, but one or more of the HV filter capacitors will typically be getting hot if so. Good way to die, touching a high-voltage capacitor before it's safely discharged.
Tube can do this, too. Tubes that got pushed way too hard can have separated spot welds, allowing metal parts to change shape as they heat up.
Or you may have all three of those problems and another one I haven't thought of to boot.
73
Can relate to the analogy having been a auto and diesel mechanic for 45yrs.I do like my fingers and heartbeat.Plate tune is the same when it drops.A couple of tubes are very used and discolored.Capasitors are old and i am sure tired.It is operating good.Working on tube replacement and cap replacement and see what happens.Others do not notice a signal lose.One step at a time.Will post results.Thank you for the response.
Back in the day, I had a new Firebird 500. 6LQ6 tubes. Even when new never did over 400-450 watts, Still a nice amp. Not into tube amps much any more, but for 100 bucks, I'd have snapped it up too.
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I have a old firebird amp + fireberd ANT SELECTOR and a OLD set of 6LQ6s that were checked at 75 to 80 % good in a box in the closet that anyone can have at a good price . The amp has a set of 6LQ6s in it now the others are extras in a another box . PM me if your interested .
Do you have a price in mind?Would you happen to have any pics?Where are you located? Sorry for all of the questions but are a weighing factor.
I am running the old girl with a Bearcat ssb and a imax 2000.I get a lot of people saying it is loud and clear.I have poeple close that radio and they say it is clean.I have talked all over the Country and outside so i can not complain with the performance.
I have replaced the tubes in this unit with nos tubes.pep 450 to 475.Helped there but still dips.Still has original caps in it.Could the older caps be causing it to sag and come back up after a couple on seconds?
I once forgot to discharge a firebird 500 before replacing the caps and tubes many years ago. Blew myself about 5 feet till a wall stopped me, collapsed, peed myself and felt like my heart exploded, and had a nasty scorched hole in my finger where all "get out juice " went. I don't recommend experiencing this. Be careful, those old buggers bite hard.
Well changed the caps and diodes.Still has a dip about 3 seconds into the key.Caps are not heating up.I tried.
One possible culprit is the blocking capacitor between the tube anodes and the Plate Tune control. Usually a disc ceramic. But it's easy to tell. The position of the Tune know where the power peaks will change after the 'sag'. Typically this restores the power seen at cold keydown.
Don't see it a lot, but it's easy to check this way.
73
Don't see it a lot, but it's easy to check this way.
73