I opened My F6 up and replaced the burned R4 (18R) with a new one. Hooked up power and checked bias, was a bit high at ~ 0.6 V, then I noticed that R4 was very hot, lots of current going through so something else is bad. Looking at the schematic I'm taking a wild guess that Q1, or Q2 might have failed. All other components look good visually. I have a few spare IRFP240s in my spare parts so I'm going to replace both Q1 & Q2. Does anybody any other ideas ?
Paul
Paul
If output offset is that high then that means high across one of the Jfets?
That Jfet possibly cooked too?
Hi Zen Mod,
Before I saw your response I had already changed out Q1 & Q2, still same problem, R4 getting very hot, just blipped on the power briefly, I quess the Jfets are cooked like you suggested. At this point I think I'll just repopulate the entire board in case something else has been compromised. Is there a chance that the input transformers have been damaged ?
Thanks,
Paul
Before I saw your response I had already changed out Q1 & Q2, still same problem, R4 getting very hot, just blipped on the power briefly, I quess the Jfets are cooked like you suggested. At this point I think I'll just repopulate the entire board in case something else has been compromised. Is there a chance that the input transformers have been damaged ?
Thanks,
Paul
Small update on My F6 build.
Initially I wasn't happy with the sounds it produced... seemed as less than expected
Nothing wrong with my build or my speakers (checked everything to be sure)
Finally removed my George Wright penned tube/triode preamp..(which worked well in my preceeding setup).. fitted a 10 k Stepped atten cobble up as a rudimentary volume control ..a simple experiment.
INSTANT wonderful sounds.. a genuine Night And Day difference.
This one helluva good amp.
Sweet, Rich, exquisitely Detailed sounds.
Hearing is believing.
Matching seems as key and Good gear may not prove so good.. when the other bits are far better
Initially I wasn't happy with the sounds it produced... seemed as less than expected
Nothing wrong with my build or my speakers (checked everything to be sure)
Finally removed my George Wright penned tube/triode preamp..(which worked well in my preceeding setup).. fitted a 10 k Stepped atten cobble up as a rudimentary volume control ..a simple experiment.
INSTANT wonderful sounds.. a genuine Night And Day difference.
This one helluva good amp.
Sweet, Rich, exquisitely Detailed sounds.
Hearing is believing.
Matching seems as key and Good gear may not prove so good.. when the other bits are far better
Small update on My F6 build.
Initially I wasn't happy with the sounds it produced... seemed as less than expected
Nothing wrong with my build or my speakers (checked everything to be sure)
Finally removed my George Wright penned tube/triode preamp..(which worked well in my preceeding setup).. fitted a 10 k Stepped atten cobble up as a rudimentary volume control ..a simple experiment.
INSTANT wonderful sounds.. a genuine Night And Day difference.
This one helluva good amp.
Sweet, Rich, exquisitely Detailed sounds.
Hearing is believing.
Matching seems as key and Good gear may not prove so good.. when the other bits are far better
Build yourself a BA3 front end as preamp, it compliments beautifully. Glad your amp is pleasing.
Russellc
Although BA3 has fairly. High output impedance, it still compliments beautifully.
Russellc
Good advise.. I Will get on it.. Thank you for the suggestion..
Yess.. this F6 build is definitely good in MY ears.
No more second thoughts whatsoever.
Not getting too much heat out of the heatsinks 10" x 9" x ~3" though.. 45C on my IR thermometer.
Some noticeable heat drifting up from the currently lidless case though.
Having to give some considered thoughts to a heat transparent lid.
A flat sheet lid is clearly not appropriate.
Bias is at 5.5 volts. Any point/advantage in adding more?
As in: will it sound audibly better with more bias.. or merely into diminishing returns ?
Odd about my Pre.. as it has worked well in previous setups. But it's also 12 yrs old.. if that has relevance.
Doesn't matter a whit though.. as a simple /silly Pot and wires is doing.. Far.. better than my Pre managed with this F6
No notion as to why.. irrelevant.. as I'm mainly interested in results.
It's now working and Sounding better than I've had in My setup in 40 years.. What's Not to Like?
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Yes, the F6 isn't as hot as others...I did not notice improvement over standard bias, I think mine is a tad over standard. I think .6 or so.
You will love BA3 front end.
That will depend on your speakers.
If they are 8Ohm FR drivers with better than 93dB sensitivity, then unlikely to notice any improvement.
If they are regular 8 Ohm 87dB speakers with crossovers then possibly yes.
If they are 4 Ohm 87dB speakers then highly likely yes.
Ahh thank you gentlemen.
More than happy with it's current performance.
Don't want to mess with it .. just yet.
I've only recently got it working
Drivers are obstensibly 8 ohm and 95 db. (measured by others as 5.6 ohms in use)
Starting to hunt up BA3 info... while waiting on the bits for my ' Ultrasimple mm/mc RIAA preamp 2' phono cobble up.
More than happy with it's current performance.
Don't want to mess with it .. just yet.
I've only recently got it working
Drivers are obstensibly 8 ohm and 95 db. (measured by others as 5.6 ohms in use)
Starting to hunt up BA3 info... while waiting on the bits for my ' Ultrasimple mm/mc RIAA preamp 2' phono cobble up.
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F6 all better now, replaced the Jfets and everything else except caps and transformers just for good measure. Up biased and singing again. In another thread Nelson hinted that tube gear could cause voltage spikes on shutdown high enough to wipe jfets. I have an Aikido pre feeding the F6 so this might be a cause for the jfets failing so soon. Need to make sure to always shut the amp first and start it last which is what I normally do, but I also need to keep others that don't know better from touching my gear. Now I need to finish up the M2 to see how it compares.
PJN
PJN