My Simple SE was my first build, and I only ordered enough valves to fill the board. A spare set would have been helpful, but I did not want to invest too much in case I did not like it. But now I have been bitten by the bug and generally have enough valves to try something different if I suspect a faulty valve. Unfortunately, I don't have any ECC82/12AU7 to sub in to see if it makes the gain as low as you describe. Maybe someone else with a Simple SE who has a 12AU7 available might like to see if they get similar results to you?
I would also check the board for any obvious mis-wiring, solder bridges etc. As you have the same symptoms on both channels, you have either made the same wiring or component mistake on both channels, or it is a problem common to both channels (or there is no problem at all with the amp - eg speakers).
If the problem is NOT a component problem (you said you checked resistor values), then it is either the power supply (common to both channels) or the input valve. Have you checked that you are getting the right voltages?
I know it might seem like a pain in the neck now, but when you get this thing working it will be worth it, and you will have learned something!
Chris
I would also check the board for any obvious mis-wiring, solder bridges etc. As you have the same symptoms on both channels, you have either made the same wiring or component mistake on both channels, or it is a problem common to both channels (or there is no problem at all with the amp - eg speakers).
If the problem is NOT a component problem (you said you checked resistor values), then it is either the power supply (common to both channels) or the input valve. Have you checked that you are getting the right voltages?
I know it might seem like a pain in the neck now, but when you get this thing working it will be worth it, and you will have learned something!
Chris
chrish said:
Only voltage check I have made thus far is B+ just before the CCS semiconductors. I'm showing ~460V.
I've been over the board many times and do not see any wiring or component issues. At this point, I suspect inefficient speakers or inferior input tube. As Ty said, it would appear the input tube is a Russian 12AT7 but there is really no way of knowing. Mine came from a tube dealer on eBay in an OEM box so who knows. I bought it from him because he had a good deal on tube sockets I needed so I wanted to save on shipping. Should have just ordered one from Jim McShane when I ordered my KT88's from him.
What kind of (peak) voltages do you see if you stick your AC voltmeter across the speaker terminals?
Do you have either side of the output transformer's secondary grounded to chassis? It almost sounds like you might have a short there.
Ty_Bower said:
Roger, I have the common side of each secondary grounded to my earth lug as shown on George's wiring page. 8-ohm goes to speaker positive. I will verify all of these connections later this afternoon.
Well, I removed the grounds from the speaker terminals and there's no difference in operation. 😕
see if you could try different speakers? you never know the answer could be something more straight forward
Did you try bypassing the volume pot? Are you running a source that has volume control on it?
ERRRR...nevermind...reading through earlier posts and this was already suggested...sorry...
ERRRR...nevermind...reading through earlier posts and this was already suggested...sorry...
cjkpkg said:
Roger. This is one of the first things we did. Volume pot has been disabled for most of this testing. All three sources (Computer, iPod, standalone player) exhibit the same problem so I think we have ruled out the source device.
dubdub said:
I'm beginning to think it's the speakers but, as a newbie, I don't have any other speakers to try. Nate is going to mail me some different input tubes to try and see if that is the problem. Failing that, I'm going to try and arrange to bring it over to Nate's.
N1ESE said:
I might of missed it but what tubes are you using at the moment?
I think that as the Simple SE is a single ended amp, the power is not going to be as high as a push pull design. The best way around this is some efficient speakers that are easy to drive-perhaps you were thinking of upgrading your speakers anyway?
If anyone has any suggustions for affordable speakers? Im looking for a pair for my (almost finished) simple SE as well
all the best!🙂
dubdub said:
I'm currently using a pair of KT88's but I've also tried it with a pair of EL34's when I initially tested the amp at first power on. Same volume issue with either pair of output tubes. I realize it is a low power SE amp but others are reporting much higher volume levels than I am experiencing.
I am planning on more efficient speakers, I just wanted to get the amp built and working properly first. I'm planning on a pair of Fostex 127en drivers in a Fonken Floorstander Mk II cabinet.
I don't think it is the speakers. I hooked my Simple SE up to a set of Vandersteen 2Ci last night. They are not know for being efficient speakers - probably around 88 dB at best. The Simple SE was plenty loud with them.
There should be much more than 100 mV AC at the speaker terminals. With a 1 volt input signal you should be getting about 10 volts out.
There should be much more than 100 mV AC at the speaker terminals. With a 1 volt input signal you should be getting about 10 volts out.
Be damned if I know what's going on. I wish George was around, I haven't seen him in awhile. I hope he is doing ok with his illness. 🙁
Would you consider yourself safe to take voltage measurements on the amp while it is running? We can verify that some basic parts of the amp are working correctly. Measuring the DC voltage at the top of R10 (with no input signal) should give 2.2 VDC if the CCS is correctly sourcing 10 mA. Check R20 to verify the other channel.
Again with no input signal, the DC voltage on one side of R17 should be about 40 VDC (assuming you've got a 560 ohm resistor and are using KT88 tubes). That would indicate the output tubes are properly biased around 72 mA at idle. The other side of R17 is at ground, so if you read 0 volts you are on the wrong side.
With a full scale signal applied to the input RCA jacks (~1 volt AC) you should have over 50 volts AC on either side of R16. That's the signal going into the grids of the power tubes. If you have much less, the 12AT7 probably isn't working correctly or there is a component error around the driver tube. Check R26 to verify the other channel.
Again with no input signal, the DC voltage on one side of R17 should be about 40 VDC (assuming you've got a 560 ohm resistor and are using KT88 tubes). That would indicate the output tubes are properly biased around 72 mA at idle. The other side of R17 is at ground, so if you read 0 volts you are on the wrong side.
With a full scale signal applied to the input RCA jacks (~1 volt AC) you should have over 50 volts AC on either side of R16. That's the signal going into the grids of the power tubes. If you have much less, the 12AT7 probably isn't working correctly or there is a component error around the driver tube. Check R26 to verify the other channel.
With no input signal, the voltage on either side of R13 should be 202~205 volts DC.
If you measure it and see that it is more like 360 volts, that means the CCS is running wide open, not dropping any voltage at all. That would indicate a problem with the "12AT7", not necessarily a fault with the CCS.
If you measure it and see that it is more like 360 volts, that means the CCS is running wide open, not dropping any voltage at all. That would indicate a problem with the "12AT7", not necessarily a fault with the CCS.
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