As much as we like tubes, we also have to take into account the sad fact that they do not last for ever.
When designing our units, we go through a lot of effort to treat our tubes in such way that they are not heavily loaded or exposed to straining conditions. That, combined with our use of high quality tubes – most often mil grade – makes for constructions where the tubes tends to last a very long time. Several of our original prototypes in our studios still run on their original tubes – after 15-20 years of near-daily use. But off course, with complex and fragile stuff like tubes, there’s simply no way of predicting exactly how long they’ll last.

Which means that you can’t use a timer to know when it’s time to change tubes. So how do you know?


Main symptoms of tubes wearing out include:

  • Sudden drop in level on one channel in the dB magnitude
  • Sudden rise in distortion at high levels in one channel only
  • Heavy microphonics, that is, knocking on the box or operating switches “pings” into the audio clearly
  • For the vari-mu compressors: Gain reduction in stereo mode gets uneven, reducing much less in one side than in the other across the first 5-7dB GR

Should you experience such trouble with your Gyraf, it’s probably time to think about replacing tubes.

In our designs we run none or very low grades of feedback, which means that for precision in levels we depend on using tubes that are properly matched for gain and plate resistance.

If you get your tubes locally – from your music- or hifi store – you will have to ensure good matching. Either ask for tight guaranteed matching of gains in-circuit, or try borrowing a handful of tubes in order to find the best matched pair of the lot. For remote-cutoff/vari-mu tubes it is important that the gradient of the GR curve matches decently as well – which “in the wild” is roughly a 1:10 function (meaning binning in ten groups works OK, or, in other words, that you statistically need between 10 and 20 to get a 50/50 chance of decent match).

When buying NOS tubes, please be aware that most sought-after tubes in the market today (in our case e.g. the E88CC) has been bought, tested, rejected, and sold back into market numerous times by now. It’s not your luck that has run out, it’s simple market mechanisms..

You can buy the tubes from us as well – but note that these are not stock items, so it may take a while for us to do the matching – usually when we are building a run of the unit in question anyway. Note that the prices include shipping but not VAT if applicable. The types we usually have available are:

G10/G22 vari-mu tube set – 2x PCC189 matched – DKK1200 incl. shipping ex. vat*
G10/G22 output tube set – 2x 6H23n matched – DKK800 incl. shipping, ex. vat
G10/G22 complete set – DKK1700 – incl. shipping, ex. vat

G14 Tube set – 2x E88CC/JAN6922 matched for the classic G14 – DKK800 incl. shipping, ex. vat
G14-S Tube set – 2x 6H23n matched – DKK850 incl. shipping, ex. vat

G23-S Tube set – 2x 6H23n matched – DKK850 incl. shipping, ex. vat

G25 VocalShape Tube set – 2x 6H23n, PCC189*, PCC88 – DKK1200 incl. shipping, ex. vat

*Please note that when replacing vari-mu tubes in compressors, a re-adjustment of the unit is usually required (or at least, a very good idea).

For other spare parts like knobs, screws, connectors and such – please email us

And PLEASE note: Take care with the high voltages inside the units if replacing tubes yourself. There are really dangerous voltages exposed to touch when the units are opened (!)