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I'v used this fan a few times. It drops right in, parameters similar, quiet and cheap. Just be sure to note the rotation. Sal https://www.digikey.com/product-detail/en/nmb-technologies-corporation/4715FS-12T-B50-D00/P12896-ND/740253

wow, that's pretty awesome. I'd grab some felt washers before you mount it, lol

Thanks! I’ve had a few more and here and did an A/B comparison with a 510mr I recently finished. The 500 takes the cake in my opinion. And yea, I ended up replacing the fans. The new ones are cheap and much quieter.

I had this happen on two 2500s. I just pressed it back in but one wriggled back out after taking a trip with it. Good idea to keep it in place.

hmm... James Martini. In the Maxell "blown away" picture featuring the L100s there is a martini glass also being blown away. Coincidence?

Merry Christmas everyone!

You can use your DMM to check it. You should have about a 1.2v voltage drop across it. It can be replaced with two 1n4148s connected in series, cathode to anode.

You can use 1n4737A, its 7.5v, 1w. Sal

I would replace the zeners while you have it apart. I use 30v with no issues. Might as well replace the 24v zeners on the power supplies, Q809. There is also a 7.1v on the relay board but I don't know how crazy you want to get. 24v, 1w...

No problem, and sure post a thread. This is a great amp that should be done right. I have built several of them and they never disappoint. Good Luck! Sal

Hi Terry, Here are the trimmers I used They are available at digikey.com. I used a multi-turn for the amps and single turns for the Relay board. Amplifiers: 2pc - https://www.digikey.com/product-detail/en/bourns-inc/3296W-1-223LF/3296W-1-223LF-ND/2535906 Relay board: 2pc -...

So today I did some tube matching to see what my 6CA7s were drawing. I used the Metheod in the link below which basically has you rotating tubes into a one chosen socket while leaving both tubes in the other channel and measuring the voltage on the plate resistor for each one. Looks like I have...

It's the access that I didn't plan for. I deleted all the wiring for the Pam. So to check the bias I have to flip it up on its side. PITA! I'll probably drill two small holes on the sides with contact points to insert dmm probes. I compared data sheets for different driver tubes I see people...

Been debating that option. Easy enough to do. Just have to reasearch which tubes to buy

I don't want to get too crazy with it, but ill keep an eyes on the bias difference as the line voltage increases. hindsight I should have had some hidden test points to avoid flipping the amp each time I check. I ran it for hours straight and am very happy with it now. the line voltage...

Yea my line voltage sags pretty low. I'm at 114v. Just checked the filament voltage and have 6.2v. B+ is at 400v. Just a few weeks ago it was cooler and my line was about 120v. I had 422v on the B+ then. Too many freakin variables to look out for!

Well I finally had some time to re wire this amp and make some changes. I'm laughing at myself over the drastic improvement in sound and noise floor when things are done right lol. I can almost put my ear on the cones before I hear 60hz hum. I wanted to etch a board for the big films but I...

I had some time to download the calibration manual and went through what I could without a calibrated 6L6. The revised calibration is for the 539b/539c. Everything is pretty damn close but the bias voltage. The bias meter reads about a volt lower than my fluke 87V on the 10v scale and 5v low on...

So I ended up finding a 539b for a great price. It hasn't been recently calibrated but I had a good conversation from the tech who owned it for 20 years. It's pretty dirty and the controls definitely oxidized. But I fired it up and tested the tubes in my ST-70 after I downloaded the manual and...

Alright, round 2. So when I decided to build a new chassis the plan was to reassemble the amp the same way It was originally and change the electrolytics. Now that I have a better understanding of the circuit, I need to make some changes. I bought new 20awg silver coated teflon wire and am...

I double checked this as I went. Everything is grounded to the perf aluminum. Bias pots are force threaded in. I ohmed these connections out to make sure. I had a thought and it turns out when the preamp is hooked up with no signal the bias is steady. B+ is 422v. If I pull the RCA out bias...

Ill put a scope on it after my son goes to sleep. I wish it was the meter going nuts but when the bias shoots up the tube starts singing. Not good. The problem is I jumped into it to fast. Lol. I should have ordered new wire. I also waited until after it was running to fully read the many...

So I have a bit of an anomaly... I decided to do the rectifier mod and add 2 1n4007s on the GZ34. After I warmed it up I checked the bias which was steady but as i went to remove the alligator clips the bias shot up to 4v on the left channel! it seems wiggling the wires on the front left tube...