EF86/EL84-based 18W Prototype Amp

I have about ten takers on TGP. The problem is that most of them are flippers and that is about the last thing I want to see happen to this amp. This amp will be the second amp I have given away in the last few years. The first was a 2-Channel "H" with an Avatar 2x12 cabinet. That amp went to local guy whose basement was flooded in a downpour. I do not mind giving gear away. I just do not want the person who receives the amp to turn around flip it for a profit. It does not cost me anything to keep the amp except space.
 
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I have a PRS Forum taker. The amp is going to dogrocketp.
That’s great!!! Kudo’s for doing this. A unique and special amp. And for NOT giving it to a flipper. Totally agree that when you to do something this cool, you do it so that you’ve done a kindness for someone, and not so they can flip it for profit. Well done all around!
 
I have about ten takers on TGP. The problem is that most of them are flippers and that is about the last thing I want to see happen to this amp. This amp will be the second amp I have given away in the last few years. The first was a 2-Channel "H" with an Avatar 2x12 cabinet. That amp went to local guy whose basement was flooded in a downpour. I do not mind giving gear away. I just do not want the person who receives the amp to turn around flip it for a profit. It does not cost me anything to keep the amp except space.
I've been giving away quite a bit of stuff lately and am reluctant to give it to someone who is just going to sell it for personal profit.
 
I've been giving away quite a bit of stuff lately and am reluctant to give it to someone who is just going to sell it for personal profit.
Right! Gifts are to be enjoyed and appreciated by the recipient, not sold for profit. I’d make them sign a waiver.
 
This amp is going to Pete Cage for a tuneup, and then will be further donated to Clarence “the Bluesman” Turner for a gigging amp. I got him a PRS, and I hate the borrowed amps he’s been playing through. He’s both a friend and a band mate. You can listen to him on WPFW.org. He’s live on Wednesday afternoons from 12 to 1 EST. The show is called “Don’t forget The Blues.” they archive it as soon as it is over. You can go to the website, click on the programming icon, go to archived shows and listen to it at your covenience. If it’s late in the week, go to the local music icon and scroll till you see it. PM me if you have any questions.
 
This amp is going to Pete Cage for a tuneup, and then will be further donated to Clarence “the Bluesman” Turner for a gigging amp. I got him a PRS, and I hate the borrowed amps he’s been playing through. He’s both a friend and a band mate. You can listen to him on WPFW.org. He’s live on Wednesday afternoons from 12 to 1 EST. The show is called “Don’t forget The Blues.” they archive it as soon as it is over. You can go to the website, click on the programming icon, go to archived shows and listen to it at your covenience. If it’s late in the week, go to the local music icon and scroll till you see it. PM me if you have any questions.

The amp does not need to go to Pete. There is noting wrong with it. It is playable as is, but it may need a new EF86 (the keyword here is "may," not "does"). That is a consumer serviceable part (every tube in this amp is configured for "cram and jam" use without the need to rebias anything). The problem with EF86s is that they are all microphonic to a point, which means all of them will ring at least slightly from vibration as the guitar signal drops off (one can use tube dampers and isolate the socket, but an EF86 is still going to ring slightly). It is not a problem at gigging volumes. However, it can be a problem in the studio, which is why I went with a separate head design that can be isolated from the speaker cab.

While the power tubes are original, this amp has been operated conservatively since I built it. It has only been out of the house a few times. The amp has never been operated for an extended period of time with the master volume dimed. The B+ voltage is only 305VDC +/- a few volts due to fluctuations in the line voltage depending how far one is from the transformer that steps 7,200VAC entering a neigborhood down to center-tapped 240VAC at the electric meter; therefore, it is not running the tubes as hard as a lot of vintage designs. The cathode to plate voltage differential is under the 300VDC maximum for true EL84s/6BQ5s. I built it conservatively because the standard Soviet 6P14P (what a lot of companies sell as an EL84) was designed with a maximum plate to cathode voltage of 300VDC. The only tube that could be reliably operate for a long time at 7189 plate voltages was the 6P14P-EV (a MIL-SPEC Soviet version of the 6P14P). The 6P14P-EV is what Sovtek sells as the EL84M. It is the Soviet equivalent of a 7189.

The reason why I cautioned you about taking the amp directly to an open mike without a backup is because it has been sitting unused for about ten years. Not using an amp is worse than playing the heck out of it because the electrolytic caps tend to degrade over time unless power is routinely applied to an amp. Most of the vintage amps that have been through my hands that needed complete cap jobs were in the best cosmetic shape due to not being used. The moral of the story is that when shopping for a 40-plus-year-old amp to use as a daily driver, look for amps that look like crap from the outside. They tend to be the amps that were loved enough to keep the caps formed. This amp is only 25 years old and it is was fired up on regular basis for the first 15 years. One thing that I would definitely replace if you plan to gig with the amp is the fuse. It currently has a 250VDC/2A slow-blow fuse in it. I would replace it with a 250VDC/1.25A slow-blow fuse if I was going to take the amp to venues on a regular basis to ensure that the fuse blows before the power transformer in the case of a catastrophic power tube failure. I only had 2 and 3A slow-blow fuses on hand when I built it. The power transformer is rated for 83VA, which is less than one amp of current at 120VAC.
 
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You should be able to get a 1.25A/250V Slow-Blow 3AG-size fuse at Chuck's. They usually come in packs of 5. If Chuck's does not have 1.25A/250V Slow Blow 3AG fuses, Mesa sells them on their site for $1.00 each in quantities of 5 because, once again, that is how they are packaged from the manufacturer. You will also have to pay shipping, but I would check with Chuck's first. This fuse has been used in every 2xEL84 amp Mesa has ever produced and Chuck's was one of Mesa's original dealers.

It is important to get slow-blow fuses and not fast-acting fuses. A tube amp experiences significant inrush current when it is powered on due to the need to establish a magnetic field in the power transformer. A slow-blow fuse has a built-in time delay to accommodate inrush current demands before it blows.
 
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