Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: Ascari on January 19, 2021, 12:29:24 PM
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It appears my Eros has given up the ghost. When I turned it on today, no sound. The Beepre is fine. After checking, at least one of the E86 tubes was bad. In the process of checking, I destroyed the second. (Don't Ask) Since I had a spare set I installed the spare and viola it was working again. At least I think so. After a few minutes I realized only one channel was working. Hmmm. I played around a little bit and swapped tubes from side to side. Guess what? Neither side is working again. My guess is something has failed and blowing the tubes. There is about 3,000 hours on preamp. OK time to start with the basics. Where should I start? I'm thinking it is the right hand channel but not sure.
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Measure voltages. Use the tubes that you think are blown. Check to see if they are glowing. The glow is very faint, you will need the lights out to see it. Once you have established if they are glowing do the voltage measurements. Report any that are off from the manual.
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My guess is something has failed and blowing the tubes.
A failed component usually gives a pop and a puff of smoke. You may just have a loose connection in the amp, which may be revealed by a voltage check. It's entirely possible that your tubes never had an issue, especially with only 3000 hours.
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I just got the manual dug out and will start this afternoon. As an FYI, there was no smoke or "pop". I was listening to music the day before and had not issues. The next day, there was not output from the Eros. I checked the tubes on a tube tester and at least one was showing a short. Can't say about the other since I accidentally put the tube into the wrong socket on the socket which resulted very bad settings. It went off like a flash bulb. For some reason it also shows a short. Anyway, I check out the extra set using the appropriate socket and settings and let you know what it says. I will also let you know the various voltages as well.
Thanks
Paul
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Can't say about the other since I accidentally put the tube into the wrong socket on the socket which resulted very bad settings.
That could definitely cause some damage.
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The plot thickens. I checked all of the resistance at the rails and they were in a hair's breath of the original settings. As far as the tube sockets, they too were pretty much the same except for one resistance on the c socket. One had gone up about 6K Ohms. I left the numbers upstairs and will get those toy you. All of the DC voltages were in normal spec and all 4 led's lit up on the three boards. Now for the interesting part. I rechecked all of my tubes. (I have a B&K dynascan tube tester.) Except for the one that I blew up, the other three showed good. I came back down to my system plugged everything back in. Put on a record and I got sound out of both channels, however it was very low at full volume. The longer I left it on, the quieter it got. The turntable I am currently using has a low output MC with a passive sut. I purchased the sut from a gentlemen on eBay who makes them. It is about 4 years old. I thought it might be the SUT so I by passed it plugged the directy into the Eros. There was no change in volume. In fact it was dead silent. As an fyi, prior to purchasing the SUT I used the same cartridge with the EROs and got descent volume but just not enough. Finally just to rule out any issues with the Beepre, I moved the Eros ouput to my CD input on the Beepre. No change.
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Diminishing signal output would generally mean that voltages are moving around. You'll need to capture voltages after this has happened and we can help you determine what might be going on.
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I plugged the unit in and took an initial DC Measurements. I then waited for about 10 minutes and took them again with no change.
Right Left
Kreg 4 volts 4 volts
Ob 137 V 137 V
bA 0 V 0 V
breg 137 V 136V
Oa 142 V 142 V
Ia 219 V 219 V
With those numbers I decided to double check my resistance measurements on the tube sockets
I discovered a potential issue.
Socket A Socket B
Pin # 1 27 K 27K
2 0 0
3 75K and climbing 3K and climbing
4 Infinity Infinity
5 0 0
6 75.1K 75.2K
7 0 0
8 Infinity Infinity
9 47K 47K
Socket C 2299
1 46.8K
2 75.3K
3 26.8K
4 Infinity
5 0
6 46.8K
7 0
8 Infinity
9 47K
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Can you post some build photos?
The 4V you have at both Kreg pads is a bit strange, which tube got plugged into which incorrect socket?
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Photos of the build. Hope this helps. If not let me know. PS, I just checked the voltages again and the are the same as before.
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I would go through and be sure things like the leads of the 47K resistors aren't touching other leads that cross over/under them.
The 4V at Kreg means that the DC servo is trying to pump the brakes really hard on letting the EF86s draw any current, but your 6922 plate and cathode voltages are almost shorted together, which makes me suspicious of the wiring.
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I'll go through and check and let you know. It's interesting that it has been working for 9 years and then all of a sudden. Hey stuff happens.
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I checked the 47K resistors and all of the other resistors and wiring about the plate. It all looks good and nothing was touching etc. Looking very closely with a bright light, it all looks good. In addition, I took a shot and installed a fresh 6922 tube. The voltage at the kreg dropped to 3. By the way when I explained that I put a tube into the wrong slot, that was not on the Eros, but my tube tester. I will continue to trouble shoot as best I can. Like I mentioned before, this has been working for 9 or 10 years. I have not done any wiring on it for that amount of time except for adding some Mundorf caps years ago. I can continue to review the wiring which will happen, but something tells me it is a possible component issue.
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As an example, this kind of short would drag the plate voltage of the 6922 sections low and cause the servo to go high on the EF86 cathode.
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Thanks Paul. That is exactly what I went looking for, and they are not shorting out anywhere that I can see. Sorry about the photo quality. I should get my good camera out,
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Man it sure looks like those large resistors are shorted to that smaller resistor passing under them. Are you sure they are not touching?
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Absolutely.. No question, just a bad photo.
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PJ may have some other ideas about what's going on, otherwise you may need to send it in for repairs.
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I appreciate that and would have already sent it in. The web page indicates you are not doing that right now. Either way, we did some further checks starting from the beginning. So far everything has checked out. Will wait to see PJ has any other ideas.
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I agree with PB, the bias servos are not working.
The relevant resistors are on the B side of the board; R3 is the small 174-ohm resistor and R4 is the larger 27K. You have reported 137v at breg (which is connected to R4) - what is the voltage at the other end? It should be around 0.7 volts. You should see the same voltage at the end of R3 nearest R4. Can you check those voltages?
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I got a voltage reading of .9 volts from the distal side of both R3 and R4.
Thanks
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Just a bit of an update. Since this was my only phon preamp, I invested in a cheap phone preamp that handles both MC and MM. The only cartridge I currently have is a Hana SL. When I connected it to my turntable and then to the Beepre via MM, I got the exact same response and I did on the Eros. Nothing... Keep in mind I have that connected to a external SUT. Once I pulled the SUT out of the line, the MC portion of the cheap preamp worked and I had how shall I say descent sound but no where near what the Eros could produce. Me Soundsmith cartridge is currently in for rebuild and is still weeks off, so I purchased a inexpensive MM to use as a spare. That should arrive in a few days, and I will check that on the MM part of the preamp. I think there is a chance that the problem my lie in the SUT, but it seems strange to me that both sides would go out within minutes of each other.
Just a note: I checked every single resister on both sides and they have all of the same voltage within a 10th of a volt.
With this info, any further ideas?
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First thig to do is check to see of the Eros has DC on the input. Measure voltage across each RCA input jack center pin to jack outer shell with the Eros turned on. You should not see any significant DC voltage. Once you have verified this, check if the MC cart will also make sound directly connected through the Eros without the SUT in the circuit. Obviously it won't be as loud as you want, this is just to determine that the Eros is passing signal. If it works then check the continuity of each winding on the SUTs, and make sure the center pins of the RCAs on the SUTs haven't become grounded somehow.
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I checked for DC voltage at the inputs and it was zero on both left and right. I put the EROS back into the system bypassing the SUT. There IS sound coming through the system, but is is very very faint at full volume. In the past when I had done this, I could get almost listenable music with the volume at 75%. Your correct that is not optimal. After checking the continuity of the SUT's I only had continuity on three pins out of 8.
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OK, so as is often the case you seem to have two separate issues. You need to get the voltages right on the Eros, and also determine what is going on with the SUTs. An analysis of what connections might have been crossed when the tubes were swapped may help. I am headed out of town and have to run, but perhaps someone else can have a look at the pinouts and see if that could have created a problem.
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I'm not surprised and was coming to the same conclusion. The SUT's I have are Beyer dynamic TR/BV 370 215 006
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I got a voltage reading of .9 volts from the distal side of both R3 and R4.
Thanks
OK, that's too high. Assuming you still get 4v at Kreg, the 2N2222 is not doing its job. Could be solder joints on the PC board.
----------- Added 2021 Jan 26 6:20PM -----------
Looking over the whole thread again, I see some problems on the 6922 socket (C) resistance measurements. You might re-check - it's tricky to get the right pin on those smaller sockets!
* Pins 4 and 5 are the heater, so one should be zero and the other less than 10 ohms; you said one zero and the other infinite
* pin 7 should be 75K, you said 0.
* pin 8 should be 27K, you said infinite.
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I rechecked again this morning. First off the kregs were reading 3.9 volts and 4.2 volts. Haven't gone into the 2n2222's to check the solder connections yet. Either way the transistors are easy to replace. When I checked the 6922 socket this morning I was being super careful and did it from the component side came up with the following. I think we may be getting somewhere.
C1 46.8K
C2 75.4K
C3 27.8K
C4 0
C5 0
C6 46.8K
C7 75.4K
C8 27.5K
C9 0
I'm going to go in and reheat the solder joints to see if that changes things and let you know. If indeed the C4 socket is the culprit after so many years could it have caused a failure on the 2n2222's?
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With the tubes in the sockets, C4 will show as 0 ohms. If the tubes are glowing, C4 is fine.
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C4 is showing zero with or without the tube in place. They all glow when turned on albeit the EF86's are very dim in comparison.
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Not tube, tubes.
Any tube in any socket in an Eros shorts C4 to C5.
If the tubes are glowing, there's no issue there. EF86s glow so dimly that usually you need the lights off to even tell that they are glowing at all.
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I just had the two EF86's and 6922 out. When I pulled the 4th tube out it read 621 Ohms
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If the tubes are glowing, there's no issue there.
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OK. Looks like the 2n2222's then Do they have to be the bipolar metal can type?
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I would get the metal can type. Jameco has a good supply of them.
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Will do. Stay tuned.
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The Eros is alive! i replaced the transistors and viola, voltages came back into line immediately. I know this was not an easy one, but with your help and persistance it is a success. You do know that I had just about convinced my wife for a Eros 2. Maybe for Christmas.
THANK YOU all for your help.
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PS, one final thought. It seems strange to me that both transistors went out within a half hour of each other. Any guesses as to why? Is there something I should do for prevention?
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If it happened after you plugged the tubes in the wrong sockets, that is the likely culprit. Sometimes the transistors can be partly damaged to a point where they work for a while longer before pooping out.
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Thank you. That is not what actually happened, I didn't change any tubes until after the failure. Yes I did destroy a tube on the tube tester I know this thread is a bit confusing. None the less, it is working and that is all that I really care about. You have gone way beyond in helping me and for that you have you have a customer way beyond your expectations.