Since 1993 Copyright Notice

Electron Engine ™
Printed Circuit Boards by Emissionlabs

Last Update:

1. Introduction
2. Use of Triode Board (EE12) with Power Supply EE11
3. Use of Triode Board (EE12) with external Tube Tester
4. Use of Pentode Board (EE14) with Power Supply EE11
5. Tube Data Table
6. Typical Test sequence
7. About the purpose of burn in.
8. Fusing of the boards.
9. Building instructions
10. Options and Support

Pentode Board EE14, for Octal tubes.

READY FOR SALES in April/May 2024

We sell this product is a kit. We supply the bare PCB and the parts.

New made pentodes are burned in by the factory for as much as needed. It is only the moment where the tubes have developed full emission, and leakage current is at acceptance level. This This invests time and electricity cost. However before final matching, tubes need extended burn in. The EE14 board is very useful for this, because is shows for each tube, what is the plate current. So, a matched, out if the box quad, must have 4x the same current. However, matching has to be the same at variety of working points, not just at one. If matching is good at only one working point, but NOT good at other working points, the tubes have what we call a mismatch in transconductance (Gm). Which is causing this effect. Also the cut off point (so where current stops flowing) must be the same for all tubes. Sometimes a tube can not be cut off at all. Though such a tube works, it can cause problems at any time, and you have to reject it. Was all of this tested well? You can immediately verify this with the EE14 board. It may well be, burning in will give improvement, this is why we do burn in. Just you need to agree this with the seller, because burn means use hours of the tubes, and it could change the appearance of the printed stamps on the tube glass.

Even so, if the printing DOES change, you can already say, it was done too short, not at all, or at too low power. Specially if the tubes develop a smell of burned paint in the first minutes, this is indicated clearly. Consider to return such tubes, if burn in does not improve them.

Mounting the EE14 board

All boards have the same mounting holes, and use the same parallel wiring bus. So it can connected to the power supply EE11 in combination with the EE12. (small triode) board. Just for testing, only one tube board type at the time may be used.

Only ONE Pentode board may be connected to the power supply EE11. See the Notes, for connecting still two EE14 boards.

The Pentode board (EE14) can burn in, and match a Pair or a Quad of large pentodes, such as KT88, EL34, 6L6, 6550, and all tubes with this footprint and similar curves.

 

What the EE14 board can do:

• Warm-up check. All four tubes can be monitored during warm-up and normal operation. If one tube warms up too slow, there may be a hidden issue with it. If used, this tube is going to last shorter. If new, you may wonder how it passed quality control. Even when it works good after warm up, the issue is still present. Explanations may be: Totally different date code, cathode damage, grid damage, or perhaps tubes are not burned in equally long. Since all tubes are monitored simultaneously, such issues become very good visible, and it affects mainly larger kind of tubes. In any case, the explanation for the different warm up time is of interest.
• Matching. Though not really intended for this, matching can be done also, with some care. Instructions are here on a separate page.
• Matching verification. The assumption is here, the tubes are already matched. Set the pair or the quad for the plate current in the table below here. Let the tubes warm up 5 minutes, and adjust bias is needed. Now reduce bias slowly, and all tubes must behave similar. Next is the Cut-off test. If matching verification or cut-off is failed, consider some burn in period. Burn in will repair many tube defects. Besides, matching of not burned-in tubes is silly.
• Cut-off Test. It can be checked if the the plate current of the tubes can be reduced down to zero. This is also an important factory test, and any failure here, means the tube has a quality issue, and must rejected. Since cut off levels are often not a data sheet specification, the EE14 board conveniently solves this be comparing all tubes with each other at the same time. Good cut off is important, to make sure the tube tests work good at high signal. With bad cut off, the curves at the lower end are not good, and this will add a lot to the signal distortion. In some cases, tubes were just not sufficiently burned in, we have seen this with EHX and JJ tubes. If so, the problem must disappear by burn it, and it must disappear quickly and fully. In other cases there is some factory error, and the problem disappears only partially, which tales very long also. Such a tube is a reject. If simply used, it can fail badly at any time later.
• Burn in. This is done at the value from the table below here. It needs observation, specially when the tubes are improving rapidly, you need to adjust the current more often. It shows good matching, when all tubes have the same LED light pattern at any current. In several cases this condition will only build up after a burn in time of 30 minutes or sometimes a few hours. This is normal, and not related to quality.

Bias Method is mixed bias, which allows to change the bias over a wide range, and at the same moment there is good stability, so tubes will not run away thermally during burn in. Though the tubes are arranged as two pairs, for best comparison of the LED light pattern, each tube is tested individually. Meaning, if one tube fails, and it's thermo fuse activates, the other three tubes are operated normally.

 

Testable tubes	Bias	Remark
6CA7	60mA
6F6	30mA
6FE5	60mA
6G6	15mA
6GW6	60mA	Use Anode Cap
6K6	30mA	Metal Part has small DC voltage on it, if tester is on. Do not touch with tools. Use protection cap over the whole unit.
6L6 Glass	60mA
6L6 Metal	30mA	Metal has small DC voltage on it, if tester is on. Do not touch with tools. Use protection cap over the whole unit.
6V6	30mA	Only Glass version
6W6	30mA
6Y6	60mA
6550	60mA
5881	60mA
EL32	30mA	Use Anode Cap
EL33	30mA
EL34	60mA
EL36	60mA	Use Anode Cap
EL37	60mA
EL38	60mA	Use Anode Cap
EL82	30mA	With EL84 to 6V6 Adapter
EL84	60mA	With EL84 to 6V6 Adapter
EL86	60mA	With EL84 to 6V6 Adapter
KT66	60mA
KT77	60mA
KT88	60mA	Metal Ring has small DC voltage on it, if tester is on. Do not touch with tools. Use protection cap over the whole unit.
KT90	60mA
KT100	60mA
KT150	60mA	Very tight with the glass, but just possible.

 

Some Notes

1. With an external 12.6V, 10A power supply, for the heaters, also two Pentode Boards can be connected. In that case, disconnect the heater supply of the EE14 boards from the power supply, and connect the EE14 to the external power supply.