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In Reply to: RE: tubes that interchange with the CV378? posted by immatthewj on July 24, 2020 at 00:23:32
IIRC, CV378 = GZ37. The GZ37 has cathode sleeves. The 5U4GB is directly heated (no cathode sleeves). 5 V./3 A. heating is employed by both types. In combination with a choke I/P filter, up to 350 mA. can be drawn from a GZ37. Don't try that with a 5U4GB. In units containing reasonably sized cap. I/P filters, the 2 types should be "interchangeable". B+ must be taken from pin 8 of the socket, as that's where GZ37 cathode sleeves are connected.
I did verify that the pin placement was the same & that the 5U4GB did fit into the socket, but I didn't power it up.
I am on the low tech side. Are you saying NOT to try it?
Cary has been known to ABUSE vacuum rectifiers with large valued cap. I/P filters. :> ( Other than that warning, the 2 types frequently can be interchanged. A proper CLC (Π section) filter with a 30 or so μF. part in the 1st position should be fine.
Thank you Eli. As I have previously confessed, I don't have much of a handle on electrical theory (arguably a good reason to stay away from tubed stuff, but I do like the sound). I'd call Cary & ask them, but they don't answer questions by telephone anymore, & who knows when they will get back to my emails; if you could indulge me for two last questions:
1) would the AC power fuse protect it from damage if the little Cary didn't like the 5U4GEs? If one or both of the tubes simply went "Fizz-bang! End of story," I can shrug my shoulders & say, "Oh well," but if I smoke this amp, I am down to a couple of real cheap bridgeable Rotels that I don't think I can bring myself to listen to.
2) & how about the 5R4GYs, are they a safer swap for the CV378 than the 5U45GEs are? Right now isn't the greatest time for me to be spending lots of money (another reason to avoid tubes) & I've noted a much wider range of prices on the 5R4GYs than on the CV378s.
I wasn't planning to be running CV378 substitutes on a long term basis, just long enough to get over a couple of humps, & I actually have found some CV378s from a dealer for $100 a pop, & some on Ebay even cheaper that I can probably do in a couple of weeks without hurting myself.
Hey, Eli, thanks again for the help on this!
The 5U4GB is a much safer swap. Forward drop in a 5R4 providing 250 mA. of B+ is a whopping 67 V. :> ( Also, the 5R4 is less tolerant of a good sized, if not huge, capacitance in the 1st filter cap. position than the 5U4GB.
Study the data sheets of the 3 types being discussed.
Thank you, Eli. I put the 5U4s in, crossed my fingers, flipped the switch to 'ON', & I had a pretty decent evening. A pair of CV378s is on my list, & it's a pretty short list, & after that I'll keep the 5U4s for backups. Thanks again.
If 5U4GBs are working well, I would not bother with rounding GZ37s up. They are out of production and carry HEFTY price tags that will only get worse, over time. OTOH, New Sensor is currently manufacturing 5U4GBs and selling them under the ElectroHarmonix (EH) label. New Sensor's product enjoys a favorable reputation. Also, OS GE 5U4GBs remain "affordable", at least for now.
The cheapest (besides E-bay, & those were used tubes on Ebay) I've seen CV378s is $100 a pop from tube depot.
From everything you typed previously, the CV378 sounds, to me, like it should be a better tube because of the cathode sleeves.
I did price a bunch of 5U4s from a bunch of different vendors (I will check New Sensor after I finish this post) & I could have quite a few spare 5U4s to burn up for what a pair of CV378s would cost me.
ON EDIT: I just checked: $30.40 each from New Sensor--I could afford to have a spare pair or two in my box of spares.
Direct shopping with New Sensor is a very bad idea. AA sponsor Jim McShane sells thoroughly tested EH 5U4GBs for less than $20 each. Jim also sells NOS GE 5U4GBs for less than $30 each.
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