Hi Everyone ,

For the 2nd time in slightly  more than 6 months , I have had to send my Avalon 737 VT off for repair .(last time it took 1 1/2 weeks to get back ..this time the estimate is 5 weeks ...yikes !!! ) I think it may be a result this time of humidity in my new studio ( which I have taken care of ) . Has anyone had "issues " with their Avalon 737 besides me ? I still love its natural sound , but I'm seriously considering the Manley mono MP40 mic preamp to replace it .  Thanks .  Shrop

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What specific issues were you having, and what tubes are you using?

I ask as in the last several weeks, I've been getting varying degrees of distortion, random clicks/pops/sputters, higher noise levels than usual, etc. in mine, which go away when I shut the unit off and turn it back on later. It's probably a tube dying, although my 737's supposedly saw little use before it got to me (for the record, I've never retubed a 737 before). If this was true, theoretically they should have plenty of life left in them since they're rated for 10,000 hours, but if mine was left on every workday since then, they should be starting to peter out about now, if my calculations are correct. 

In looking into replacement tubes, I've seen all sorts of new and new old stock variants available (6DJ9, 7DJ9, E88CC, etc) that in theory should be swappable for the stock Electro-Harmonix 6922EHs that Avalon sells, and from what I've read, they're apparently pretty adamant that users should replace with. Initially, I thought this might just be a money grab on Avalon's part, but I've seen mentions online from those more technically schooled saying that some of these swaps may indeed not be one-to-one good for this application after all - they'll fit and work, but could cause issues later. For instance, while the 6922 is essentially a heavier duty 6DJ9, it's got a higher heater voltage, and if you're using the latter you could theoretically cause power supply or other problems. 

Apparently some other mike preamps are engineered to such incredibly high specs and tolerances that they're incredibly finicky and need a specific brand/model tube, and almost nothing else will work, and some theories I've read say Avalon may have done similarly here, designing around the commonly available modern-spec 6922EH, which makes me wonder if the other most common 6922 (really an E88CC) made by JJ in Slovakia is usable or not. 

Anyway, I digress....are you using stock EH 6922 tubes, or NOS, or others, or have you ever experimented or heard about any of this?

Hi Scott ,

I have never even thought of replacing the tubes myself ( which was the problem according to Avalon ) . I wasn't getting any pops or hisses ..it just died !!  If you find a great place to get the appropriate tubes ..please let me know .Thanks.



Ouch - always suspect tube damage or death first before sending a tube unit off for service...many times it's the issue, and much faster, easier, and cheaper to fix yourself! It's pretty simple to do, and should be done with the 737 unplugged and cool. Just pop the top off (there's about 10 small screws so be careful), find the 4 glass bottles on the lower left, pull each one out gently and straight upwards. Replacements go in with equal care so you don't bend a pin or put undue pressure on the circuit board, and always advisable to use gloves or a clean towel when handling tubes (keeps hand oils off them, which can shorten life) and test everything for several hours before putting the top back on. 

The saddest thing is that unlike the old days, there's hardly any indie electronics stores around with a machine to test tubes anymore, so unless you can isolate the bad one by a burned out filament or the good ol' microphonic tap test (which can actually shorten their life or even kill iffy ones that are just hanging by a well-worn silvery thread), it's probably best to change the whole lot at once for consistency.

Regarding places to get tubes, I believe Avalon sells matched sets of the Electro Harmonix 6922s for around $80 before shipping, and hear they even number them for the specific socket they need to go into...wow.

If you're on a budget and not a stickler for the "must have factory-only" treatment, I've seen new standard (non-gold pin) quad sets of the same on eBay for around $50-ish before shipping from a storefront named Yenaudio claiming they also extensively test/match. Most vendors seem to charge about $5 above the cost of each tube to do this, which isn't a bad idea considering the factory matches theirs. However, I have no idea how extensive their testing and how optimal their matching might be for a 737 (if it's even a factor at all).

The same seller also sells tested/matched quads of the aforementioned JJ 6922/E88CC for a few bucks cheaper - I'm curious about these not just for the pricing, but moreso in that they're allegedly the modern day tube that sounds closest to the "new old stock" sound a la vintage Telefunkens and similar well-regarded old-school European brands. JJ tubes in general seem to have a reputation for being a bit warmer/midrangier (they're stock in Eddie Van Halen's new guitar amp, for instance), which is what I'd like to lean my sound a bit more towards. That said, I've also seen some random complaints about quality and noise issues with JJs too, so I'm doing a bit more research before I pull the trigger on a set. Since getting a set of both EH's and JJ's would only run a little bit over $100, I'm actually considering getting both and comparing them if the JJ's can be safely used...


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