Tube Testing

Every voltage gain Tube is thoroughly tested. The testing number(s) are marked as a % of NOS (new old stock) Gm (mutual conductance) on your tubes.  For most tubes NOS = a nominal 100 or 100%, however, depending on the tube it can range from 80 – 120.  We only sell good testing tubes – period.

Power Tubes are tested for idle plate current (mA) on our Custom Power Tube Tester at normal operating voltages for that tube.  This number is marked as mA on your tube.  This is the industry standard test for power tubes. 

Matching is done automatically, and is a Free Service!

Extended Testing: Most tubes are also listened to “Live” to ensure low noise and quality sound – Testing numbers only get you halfway!

Purchase Guarantee

Vacuum Tubes:  If a tube is defective within 45 days of Purchase Date it will be replaced.  No Returns or Exchanges.

NO WARRANTY for  Commercial Use of Tubes.  No Returns or Exchanges

Kit Amps are guaranteed to be complete (except tubes), should you be missing a part or have a defective part, it will be replaced and shipped on the next shipping day.  No Returns or Exchanges.

Kit Amps – Prebuilt are guaranteed to be free of defects for a period of one (1) year from the date of purchase. Should you experience a problem please contact us (mellowtoneamps@protonmail.com) and we will work with you to help fix the problem. No returns or exchanges, unless pre-approved. Return shipping is the responsibility of the purchaser.

Tube Labels, Re-Labelling, Re-Branding

All Tubes ordered are Guaranteed to be made by the manufacturer listed. It is however very common for a vintage tube to be re-labelled or re-branded, the only difference is the label, everything else about the tube is identical – there is no difference.  Tubes that are re-branded or re-labelled can not be returned, simply because the label is different.  We would note that roughly 50% of all vintage tubes ever made are re-labelled or re-branded.