ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Further to the above....when i search "All Transistors. 37740 Datasheet" it states MIN hfe should be 140 which puts both of mine out of spec.
Next up right channel power output transistors.....green text
left channel power output transistors.....green text
Left stage is just about in spec, should be hfe 20-70 I believe....measured these by disconnecting from the circuit board as I thought it looked easier than disconnecting at the transistor base...….left stage low
Second left stage also low......
right stage looking better...….
Second of the right also looking good......
So....I have ordered a bunch of BC550B and BC560B to replace the black tops....I have also 2N5320 and 2N5322, this said I feel I should also change the left stage 2N3055 devices, Martin I'm looking at you could you let me have a couple from your bottom draw?
Craig
Craig: So....I have ordered a bunch of BC550B and BC560B to replace the black tops....I have also 2N5320 and 2N5322, this said I feel I should also change the left stage 2N3055 devices, Martin I'm looking at you could you let me have a couple from your bottom draw? Craig
Sure you can Craig, - but why do you question the original ones?
Martin
Craig,
If I were you, I would just change the IC 423 for now. When everything is in order, check the output level difference between both channels and see if this is manageable with the input potentiometers. Now, I can't see the output transistors. Are they all original? Were they replaced on the left channel?
You may consider taking the 2N3055 from the power supply if they show a better HFE figure and send those to the left channel? Just a thought...
Ok...time to demonstrate my ignorance yet again I thought that the transistors with the low hfe would cause an imballance on the output and that the ideal would be all transistors within 20% of each other......I'm more than happy to retain the ones that are fitted if the advice is to do so....and it clearly is.
From what I'm hearing here it sounds like the hfe (and therefore the condition of the measured transistors) is good for all but one.....so therefore I will go ahead and replace the black tops and the one offending 37741 (453) sat at hfe 26......
Look at this.....devastated when I opened up the package from Frede! was well packed too....I suspect the tube it was packed in was squashed by something very heavy, asked Frede if he has any spare lens but thought I would put out an appeal on the forum in case anyone has such a rare thing they no longer have a use for, on a lighter note the panels themselves are tremendous
Sadly moving on......the replacement 2N5320 & 2N5322 also arrived today. The wayward 37741 (423) with the hfe of 26 has now been replaced with a 2N5320 with hfe of 135...its much higher than the previous incumbent, which when I removed it fully turned out to be a 2N5321 and not a 37741 at all, someone has been here before me, similar hfe to the 2N5320.
Just to follow up on your third last post. I tried to simplify the transistor HFE vocabulary but I'm afraid that I might have introduced the wrong words. The transistor HFE is the current amplification coefficient. When used alone, a low coefficient is not really a problem but when used in a multi-stage configuration, bad things can happen because the current is not high enough to drive the following transistor. I know for sure that an underpowered transistor will introduce distortion but might also cause other undesirable behaviour, which I’m not knowledgeable enough to explain.
For the 2N5321, it might be a very close cousin to the 2N5320. Check on All Transistors and compare the data. It should be very similar with better specs but not under.
I have a used facia here I can send over to you. PM me for this
Craig: Look at this.....devastated when I opened up the package from Frede! was well packed too....I suspect the tube it was packed in was squashed by something very heavy, asked Frede if he has any spare lens but thought I would put out an appeal on the forum in case anyone has such a rare thing they no longer have a use for, on a lighter note the panels themselves are tremendous
I am sure Frede will come up with something, when I see things like this I get so angry, had it myself a couple of times, ignorant package handlers, here in Mexico I never use Mexpost, they brake it, steal it or it never arrives. I am following with great interest Craig, so keep them coming
Collecting Vintage B&O is not a hobby, its a lifestyle.
Jacques
chartz:Hi, Other than that, excellent work Craig, but I think replacing transistors just because of a bad HFE is a bit overdoing it
Other than that, excellent work Craig, but I think replacing transistors just because of a bad HFE is a bit overdoing it
Jacques,
By no means I want argue with something so subjective but I think the following thread is interesting. I had myself a situation with a Philips amp where the DC offset was huge and had to replace the differential transistors to match them. That alone fixed the issue.
https://audiokarma.org/forums/index.php?threads/hfe-matching-on-transistor-subs-important-for-comp-pairs.757654/
I’ve never had the problem myself to tell the truth but I guess it all depends on the configuration.
Thanks for the link 😀
Moving on.....Frede is posting me a replacement lens, bless him...such a gentleman, I will glue it into place when it arrives. Meanwhile I have replaced the pre-amp blacktop suspect devices...
During this exercise I came across this modification that had previously escaped my attention....seems our mystery techie had identified a problem with a SE6002 and replaced it with this...……..
It is a BC149 and to be fair to our friend was still in good shape, I have no reason to believe it was causing any issues.....
It can be seen here in-situ...I think its in the Tape input
Peter paid me a visit last week and collected his things, and as he does dropped off a couple if things for my further entertainment, so I took the opportunity to test the work so far with his Thorens deck...……..
Sounds amazing...…...
Slowly working through the amplifier board, replacing the black top transistors and capacitors.....both corners of this board where broken, the bits where still in the cabinet so I'm going to cut a piece of old circuit board and epoxy it in place, so far none of the black tops measured poorly.....but on Frede's advice they are coming out.
chartz:Yes, and a joy to behold too. It looks superb in black too. Doc keeps showing off his amazing deck, but it’s entirely worth it 😊 Prices have skyrocketed over the years unfortunately. I shall keep being content with my Beogram 4000.
Doc keeps showing off his amazing deck, but it’s entirely worth it 😊
Prices have skyrocketed over the years unfortunately. I shall keep being content with my Beogram 4000.
The 4000 is an engineering delight - the 3000 is very simple in comparison. The sound is however very different.The bass extension on the 3000 seems much more - I wonder if this is acoustic feedback, though the platter weighs a heck of a lot, or whether it is due to the rubber mat. It would be interesting to hear a 4000 with a record clamp, though clearly this would rather wreck the looks! Do you remember the 4002 with the grado cartridge and glass platter?
Peter
Yes I do remember. It looked odd but not so bad. I think that Grado shamelessly copied the B&O SP cartridges, which I can tell because I opened a Grado and saw what’s inside!
The TD124 is renowned for its awesome bass.
Amplifier board now complete, all caps replaced and all black top transistors replaced also.....decided a test was in order with Peters Thoren......left channel sounds great....however, the right channel is mostly silent. Sound can be dimly heard, when the balance is fully to the right, along with a lot of noise! so something is amis on the right side, a quick check identified all the caps where in the correct orientation for polarity, its worth noting that the printed circuit board diagram and the actual circuir diagram in the manual dont agree in at least one location, and I'm happy that the replacement transistor choice is good as the left sounds fine,so I need to check the new transistor pin outs and possibly the capacitor values...I may have got one wrong.
Check those broken PCB corners.One PCB corner has the supply to one channel running very close to the edge, easily broken.Ref. my post of 21-3-2015https://archivedforum2.beoworld.org/forums/t/5230.aspx?PageIndex=4
Cheers Martin.....will check those corners out in more detail when I get home this evening, I will repair the corners as per your thread. Both channels worked fine before I started on the amp board, so I'm suspecting something I have overlooked or got wrong, the signal generator and scope may need to be dragooned into service if nothing shows itself visually, what would be a safe voltage level for the signal gen when inputting a sine wave into the PHONO input, very low im guessing ?
Yes, very few mV.Start low and use the working channel for signal level reference as you measure along the signal path.
Ok.....didn't get a lot done this evening due to prior engagements, did however get the sig gen set up and the scope and was able to make a start by injecting a 4khz signal into the phono input one channel at a time, I may try both at once tomorrow and get both traces up at the same time.....took preliminary measurements at the output of the pre amps left and right
Left channel trace...…...
Right channel trace....both look very alike so im thinking that up to this point the right channel is good...…..
Moved on to the tone control amps and found this discrepancy...……...
left channel trace at cap 106.....
same channel at the emitter of transistor 112....looks fine
Same measurements on the right channel......cap 148 first