Tom,
I am sorry but I find it hard to believe you, The two outsided transistors are ***-about-face with each other, althought the resistors are not - or you made some fancy jumpers. It would have been much easier to desolder the transistor and turn it around.
JHL invariably works first time, and I would still say double and tripple check - Vero board is horrible stuff to work with, if you don't cut the tracks properly a hairline can mess you around for ever.
Also a 113K instead of 100K would make a slight difference, but we are talking several volts.
So where you at with it Tom ?
I had a Spice file of the JLH (one I made earlier as you do
) so I just tried your supply (no problem) but was rather surprised that the transistor types (models) made such a difference to the AC gain.
The files are here if anyone wants a play.
Tom... if you are still having problems then measure and record the voltages at each transistor for E,C and B and post the results. Also check by measurement that all the resistors are what they are supposed to be.
As Nico says, the JLH works pretty much out of the bag so something basic is amiss somewhere.
I had a Spice file of the JLH (one I made earlier as you do
) so I just tried your supply (no problem) but was rather surprised that the transistor types (models) made such a difference to the AC gain.The files are here if anyone wants a play.
Tom... if you are still having problems then measure and record the voltages at each transistor for E,C and B and post the results. Also check by measurement that all the resistors are what they are supposed to be.
As Nico says, the JLH works pretty much out of the bag so something basic is amiss somewhere.
All fixed. It was such a stupid mistake I'd rather not say. Ok, I hooked up the 2N4401's wrong. Really stupid on my part. Anyway, I removed the other 100pF until I decide to do all the suggested recommendations "(As an alternative, it is possible to reduce the r.f. response of the amplifier to give a smooth 6dB roll-off beyond 50kHz – which removes much of the need for care in the layout of components, without detriment to the harmonic distortion in the audible range, and without any audible alteration to the performance – by connecting a 1,000pF capacitor between the collector of Tr3 and the emitter of Tr4; a 1,000pF in series with 100 ohms between the collector of Tr4 and earth; and a 0.01mF in series with 8 to 10 ohms between the output (‘X’) and earth. (It should be noted that either all of these components should be added or none at all, they are not alternatives.)" The only problem I have now is I have a really bad buzz. When I disconnect the input it goes away. I'll keep poking around until it's fixed. Thanks for all the help.
Tom
I guess the reason I didn't de-solder the 3906 was because I'm a little nervous about soldering transistors. I'm always afraid I'll ruin them with to much heat. It was really a pretty easy workaround even though it would have looked better if it was symmetrical.
Tom
Absolutely important.
I had not realised just how important this tiny detail is for many years into my DIYing attempts.
A few years back I was studying a Sugden P128 Power Amplifier.
I noticed that they had connected the Main Audio Ground directly to the trace connecting the main smoothing caps. That is also where they bolted the Speaker Return. Then it clicked in my somewhat slow brain.
The trace connecting the smoothing caps was on one side of the PCB. The Speaker Return and the Main Audio Ground were on the other side of the PCB. The bolt was acting as that "short wire link" from one side to the other.
Sugden had indeed implemented the separation of the dirty ground (PSU Zero Volts) from the Clean Ground.
Here is JLH's explaination:
However, one transistor change which is recommended is the use of a 2N1711 as Tr3. This has a high voltage capability equal to that of the 2N1613, and a current gain which is double that of either the 2N1613 or the 2N697. The use of the 2N1711 instead of the former types suggested for Tr3 increases the feedback factor and approximately halves the typical distortion factor of the system (0.025% at 9W or
0.05% at full power) without detriment in other respects.
For 2n1711 replacement BD139 would have to be in highest gain group for it to work well aim at at least hfe of 130
2n1711 has FT of 100Mhz - couldn't find this figure for BD139 so not sure about that.
It would probably work OK but if you want certainty you know what to do
For 2n3905 replacement i/p device I would not use BD139 instead try a BC560c that will work better.
Good Luck !
However, one transistor change which is recommended is the use of a 2N1711 as Tr3. This has a high voltage capability equal to that of the 2N1613, and a current gain which is double that of either the 2N1613 or the 2N697. The use of the 2N1711 instead of the former types suggested for Tr3 increases the feedback factor and approximately halves the typical distortion factor of the system (0.025% at 9W or
0.05% at full power) without detriment in other respects.
For 2n1711 replacement BD139 would have to be in highest gain group for it to work well aim at at least hfe of 130
2n1711 has FT of 100Mhz - couldn't find this figure for BD139 so not sure about that.
It would probably work OK but if you want certainty you know what to do
For 2n3905 replacement i/p device I would not use BD139 instead try a BC560c that will work better.
Good Luck !
Hi
I would say that the BD139 is a better choice to replace the 2N697 than the 2N1711. That old transistor is probably not now widely available, either. The BD139 has better output characteristics (reduced Early effect distortion (higher Early voltage)) and if you are concerned about the gain, see if you can get a -25 grade rather than a generic or -16. Most samples I have used have gains of at least 100, so a generic type would be OK too.
A BC212 or BC556 would replace the 2N3906 but these transistors are still available AFAIK.
John
I would say that the BD139 is a better choice to replace the 2N697 than the 2N1711. That old transistor is probably not now widely available, either. The BD139 has better output characteristics (reduced Early effect distortion (higher Early voltage)) and if you are concerned about the gain, see if you can get a -25 grade rather than a generic or -16. Most samples I have used have gains of at least 100, so a generic type would be OK too.
A BC212 or BC556 would replace the 2N3906 but these transistors are still available AFAIK.
John
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From experiences using BD139 in fast circuits, I believe BD139 fT is very high, at least above 100M. What I didn't understand is that when I tried to find out the fT value from BD139C SPICE model by Cordell I found:
TF=585e-12
fT=1/(2*pi*TF)=272M. That's too high imo
fT of BF469, derived from TF is 225M, so lower than BD139. I found that simulating amps with BD139C gives "too good to be true" results, while using BF469, the result is too bad to be true
. I think BF469 should be faster.
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