ESE Echomatic 6SE Issues

[EddieDay]

Hi there,

I have recently purchased an untested ESE Echomatic 6SE but as expected I am having some issues.

The guitar dry audio signal is passed through fine unchanged. However, when trying to record to the tape the resulting audio is extremely poor quality, barely resembling (if at all) what was played and the Echo knob has to be turned all the way to to get an audible sound. The erase head is also not wiping the tape. So you end up with a pretty nasty noise just repeating.

I have replaced the tape, given the heads a clean (does seem to be black (carbon?) still around the centre silver sections, not on though), changed the valves to known working ECC83s and have checked over the circuit with no obvious signs of issue.

I have a small manual for IV, IVR & VI models which has a very small schematic and in low quality print, which means most values are totally unreadable. If anyone has a digital copy of a 6SE circuit diagram that would be a great help. From what I have seen through the machine seems to be unmodifed.

Next I hooked up the oscilloscope. The dry signal seems fine at R27 and at R13 (side without recording head) locations. The oscillator is also producing 50Khz. However, the audio signal on the recording head looks very low to the total peak-to-peak voltage of the biased signal. The recording head is running at 100Vpp, which I am not sure is correct or not. The erase head has 50Vpp on it, again not sure if correct or not as I do not have the full specs. But I would have thought the erase voltage should have been higher than the record? Both the record and erase are at 50Khz.

As a test I unsoldered the recording head and looked back at the R13 resistor where it goes to the recording head and the biased signal was now much better, still around 100vpp but the amplitude change was much greater than before and gave a good envelope.

I next tried using a playback head as a recording head but not much changed from when using the recording head, although the noise recorded to the tape was slighly louder.

I then checked the signal at where it comes off of the playback heads and is combined after the switch block, which should be 25mV. There was mains ripple there but on top of that was only around 2mVpp of signal.

So, I have come to a point where I am not sure how to proceed.

If anyone has the specs of the recording heads and what the peak-to-peak (or rms) voltage should be for both the recording and erase heads that would be very useful, or any other advice really on what to check next.