Regarding Replacement Fans for the 6700

Russ Ravella

I just had a typically very constructive exchange with Dan Quigley, N7HQ over on the Flex groups.io reflector. I'm one of what seems like many 6700 owners who would like to upgrade to the new 8XXX but are unwilling to give up the 6700's 8 slice capability. Steve Hicks has said an 8 slice version is possible in the future and I (we're) holding out for that as long as possible.

Of course all of the 6XXX's will become obsolete eventually and unavailability of replacement fans is a possible cause. The groups.io reflector thread addressed their replacement specifically for the 6700. I wanted to copy Dan's thorough comments here for anyone who might have missed them there and wants to prepare for that:

Since the Flex-6700 contains two fans, both should be replaced to ensure reliable operation. Even though [a problem might be] intermittent, the original fans in earlier Flex-6700 models are prone to failure, and it’s only a matter of time before they stop working entirely. Proactively replacing both fans now will help prevent future issues, especially [if] your transceiver is at a remote site. The SZ12S fans available from www.radianheatsinks.com are a good replacement.  

Pro Tip:

 Replacing both fans at the same time minimizes uneven wear and ensures consistent performance. Also, having a spare on hand is a smart move for remote stations.  

…, regarding the double-stick tape:  Given that the fans in the Flex-6700 operate upside down, the use of thermally conductive double-sided tape is crucial for both thermal efficiency and ensuring the fans stay securely attached over time. The upside-down orientation puts additional stress on the adhesion, so a high-quality thermal tape is essential to prevent the fans from detaching and compromising cooling.  

I recommend using 3M 8815 Thermally Conductive Adhesive Tape for this application. This tape provides excellent heat transfer and strong adhesion, making it suitable for securing fans in this specific orientation. It’s readily available from electronics suppliers like Digi-Key or Mouser.  

Pro Tip:  

1. Clean both surfaces (the heatsink and fan base) with isopropyl alcohol before applying the tape.  

2. Ensure even pressure when adhering the fan to the heatsink to maximize the contact area and thermal conductivity.  

If you need guidance on how to access the fans inside the Flex-6700 or tips for securing them with thermal tape, feel free to open a helpdesk ticket.  Dealing with the Faraday cage on the main board in a 6700 is a bit of a challenge. 

When ordering the fans, select these options - For mounting: No need for brass or plastic pushpins, the "None" option is correct. For thermal interface: Go with 3M 8815 pad. The thermally conductive stick-on pad is what we specify for this product.

Hope that helps,

73 Russ KR6W