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My Winter Project

Is there anything more boring in DIY amps than waiting for paint to dry? Me thinks not, at least right now.:sigh:
 
Old1625 said:
Thanks! I've got a few of them in cartons here. I hope to fiddle with them some day. Finding good ceramic or porcelain sockets for those bad boys may prove to be a challenge....:scratch2: Big thing about these--as well as the typical sweep or TX tube--is that (IIRC) unlike the 6L6GCs and 6550s the screen grid maximum voltage rating is significantly lower than that for the plate. This can complicate matters to a degree if ultra linear or unity-coupled design is one's goal.
Click to expand...

I haven't even looked at the plate/screen curves yet for the 1625... but with a lot of these tubes with reduced screen ratings, it's because the screens have lots of gain.

In a case of a high-screen-gain tube, it could be interesting to investigate running them in screen-drive mode... takes a pretty hefty driver stage, but the outputs get nice waveforms with little bias (ie, they're pretty much LOAFING even at BIG POWER levels, since they're being asked to dissipate very little)...

For ultralinear, the aforementioned TO330 transformers, IIRC, were made for 6146s... so, they should work with 1625s as well... one of the only games in town, if you want ultralinear, AFAIK.

EDIT: Looked up the data for the 1625... it refers you to the 807. Given the similarity of that tube to the 6L6, I dunno about screen drive...

Regards,
Gordon.
 
Since you seem to still be in design mode, from your numbers it looks like you are going from ~200 watts down to ~150 watts. I've seen a few nice refurbs that have taken this amp from a mono to a stereo amp. Apparently the parallel construction lends itself to an easy switch, in effect producing a pair of the MO100s on a single platform.

Just wondering if you are considering this, or if you are going to keep it mono (and eventually make a 2nd so you can match the pair :D)?
 
hammr7 said:
Since you seem to still be in design mode, from your numbers it looks like you are going from ~200 watts down to ~150 watts. I've seen a few nice refurbs that have taken this amp from a mono to a stereo amp. Apparently the parallel construction lends itself to an easy switch, in effect producing a pair of the MO100s on a single platform.

Just wondering if you are considering this, or if you are going to keep it mono (and eventually make a 2nd so you can match the pair :D)?
Click to expand...

It'll be stereo, I don't think I'll ever need more than 50 watts/channel, and especially the 150+W/chan a pair would offer.

jaymanaa said:
Maybe waiting for parts, especially that ONE part that you missed on the first big order.
:D
Click to expand...

I feel like I am perpetually ordering that part :D
 
GordonW said:
I haven't even looked at the plate/screen curves yet for the 1625... but with a lot of these tubes with reduced screen ratings, it's because the screens have lots of gain.

For ultralinear, the aforementioned TO330 transformers, IIRC, were made for 6146s... so, they should work with 1625s as well... one of the only games in town, if you want ultralinear, AFAIK.
Click to expand...

I thought the same thing about screen ratings ultralinear, but I've seen amps (I think) that use them in that mode with B+ of 400 or more...I'd hate to design an amp that does that and then later on have it destroy tubes:sigh: Maybe they would be perfectly fine :dunno:
 
GordonW said:
I haven't even looked at the plate/screen curves yet for the 1625... but with a lot of these tubes with reduced screen ratings, it's because the screens have lots of gain.



For ultralinear, the aforementioned TO330 transformers, IIRC, were made for 6146s... so, they should work with 1625s as well... one of the only games in town, if you want ultralinear, AFAIK.

EDIT: Looked up the data for the 1625... it refers you to the 807. Given the similarity of that tube to the 6L6, I dunno about screen drive...

Regards,
Gordon.
Click to expand...


Actually it is tubes with low mu g1g2 that work for screen drive. Lower is better. 3 is about as low as I've seen it though...:)

Also, the TO-350 was Acro's 6146 tube OPT. Tertiary winding for either CFB, or running the g2 at something other than B+. Given that you get the same k-g2 variation with fixed g2 supply and CFB I like that connection best.
cheers,
Douglas
 
updates

chassis and endbells are painted, waiting a while before I put the screws to it

used Rust-oleum professional black and white
 

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one more, with the frame around it (but not fixed to it yet)

almost time to put it together!!
 

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Looks really good so far, you do nice work. I too have used the Rustoleum proffesional line and found it to be excellent.:thmbsp:
 
thanks guys, I kinda nitpick sometimes, especially when I have time to. Transformers and sockets go in tomorrow, and whatever wiring I get done :D I'm gonna start drawing up schematics too as I tweak. I have a scanner to get them posted here.
 
That was the only picture I could take before my battery died last night:tears:, and that one was blurry. I hope to have one channel working by tonight. I'll take more pics, and detailed ones for stuff that might be important.
 
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