Clarify an Issue Brought up by a Reviewer of Riverstone Audio' Vacuum Tube Pin Straightener





Let me preface my comments by stating that a 1-star review that appeared on Amazon is TOTAL NONSENSE and likely from a competitor. The reviewer had some kind of axe to grind, or was simply clueless about the use of a pin straightener. Out of the THOUSANDS of pin straighteners we have sold over the past five years we have had ONLY TWO (yes, two) pin straighteners returned for ANY type of defect (one return was for damage to the tin storage box provided with our straighteners, the other for discoloration of the laser engraved logo on the straightener). Considering the number of Riverstone Audio pin straighteners that are in use by professional tube sellers, amplifier repair shops, guitarists/bands and our many customers with tube-based audio amplifiers, this is a REMARKABLY low return rate for this product and an overwhelming stamp of approval by the end users.

The primary design goals of Riverstone Audio's pin straightener were: (1) pins must be easily straightened, (2) pins must be put into proper alignment and (3) the pin straightener should last a lifetime. Indeed, as design engineers we hope that decades from now this product will be re-sold to future generations of tube-amplifier users. A pin straightener that can reliably pass the muster during years of use, MUST be manufactured from a material that is harder than the metals used for tube pins. BY DEFAULT, a misaligned tube-pin is straightened by going through the precision-machined holes of a vacuum tube pin straightener. Therefore, pins WILL rub against the walls of the straightener holes when inserted into a pin straightener - this is simple physics. As a result, a small degree of abrasion can not be avoided. Unless, of course, a lower hardness material such as plastic, aluminum or brass is used for a straightener. However, these "softer" materials will rapidly loose tolerance with repeated use. Moreover, pin straighteners made from less hard materials can cause undesirable contamination of tube pins. Lower cost pin straighteners, made from aluminum alloys with anodized surfaces, have there own set of problems such as contamination of tube pins by non-conductive Al2O3 (formed during the anodizing process) when inserted into the straightener. Anodizing is also an imperfect process for coating of very small diameter holes. Indeed, a hard anodized coating will not extend much beyond the entrance of a hole that is of the order of a mm in diameter. This fact is well known in the anodizing field. What you are left with when anodizing small diameter holes is a partial coating in the hole. A decade ago we explored hard anodizing as an inexpensive method to make pin straighteners. Although the material and manufacturing cost was roughly 1/3 of that for the hardened stainless straighteners choose, we discarded the idea of hard-anodized aluminum as it would not provide a long-lasting precision pin straightener that we could stand behind.

Riverstone Audio straighteners have ALWAYS been deburred, honed and inspected. Indeed, as part of our detailed final QC inspection, 7 and 9 pin tubes are inserted into ALL pin straighteners we manufacture - never an issue. Riverstone's pin straighteners are manufactured with great attention to detail, including a final polish to the outer surface. The main question then, is whether pin abrasion encountered when using a pin straightener made from wear resistant metals poses issues for the long-term health of a vacuum tube. The answer is NO -- the small amount amount of pin abrasion inherent in the use of a properly machined and hardened pin straightener will not have a detrimental impact on tube performance or tube life. In fact, our staff metallurgist would argue that slight abrasion can be beneficial, as it removes contamination such as oxides corrosion from tube pins, thereby improving electrical contact between the pins and tube socket (indeed, the pins of vintage tubes are sometimes cleaned by using abrasive paper or a hand grinder). Our staff metallurgist would also remind tube amplifier users that minor abrasion occurs on the surface of the pin each time a tube is inserted or removed from an amplifier socket. From an engineering perspective, the pins used on vacuum tubes are robust; abrasion and scratches on the surface of a pin will not affect either the function or the life of a tube.

The trade-off to be made is clear-- accept minor abrasion on the pins or use vacuum tubes with bent or misaligned pins in an amplifier. The answer of course, is to accept slight abrasion. What WILL negatively (and potentially SERIOUSLY) impact tube life is inserting a tube with bent or misaligned pins into an amplifier. This can be explained as follows: the primary weak point in a vacuum tube is the glass-metal seal along the portion of the tube pins that penetrate the glass tube envelope. Forcing a tube with bent or misaligned pins into an amplifier socket can cause very high bending and shear stresses along the critical glass-metal interface, which can lead to tube failure (and also cause damage to tube sockets). The initial damage along the glass-metal seal may not be visually apparent as it starts at a micro-level along the glass-metal interface, but can gradually increase as a tube is thermally cycled or subsequently removed and re-inserted into a socket. Therefore, a design tradeoff must be made; accept some pin abrasion (which occurs with ANY pin straightener), or risk tube damage and premature failure caused by bent/misaligned pins.

In conclusion, it is impossible to avoid abrasion of pins when using ANY pin straightener that has a long design life. Minor abrasion of tube pins will not affect the function or long-term health of a vacuum tube. That said, we do not recommand using Riverstone Audio Pin Straighteners on vacuum tubes with soft gold coated pins if you are concerned about minor abrasion of the coating. Also, if a customer is overly concerned about abrasion to pins for cosmetic reasons we do not recommend using pin straighteners.

James at Riverstone Audio


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