Difference between 5AR$ and 5Y3 as Tweed Deluxe rectifier

[d. spree]

I built 2 tweed deluxe amps in June and July. The first is a build from a TubeDepot kit and the 2nd from a Mission build kit. The TubeDepot shipped with a JJ 5AR4 and the Mission with an NOS US made 5Y3 (like the original amps). (The TubeDepot kit also came with a blackface deluxe reverb PT). It ran fine but as it was running a little hotter than it should it was suggested I use a 5Y3 as the rectifier. Did that and it runs great. I was wondering if anyone can tell me what the differences are between the 5AR4 and the 5Y3?

I also had to swap out the two output tubes this week which seems kind of quick - so I will watch and see it the new ones get eaten fast.

Thanks

[imaradiostar]

The 5ar4 is an indirectly heated rectifier tube which allows the cathode and anode to be very close together for minimal voltage drop. The NOS 5y3 is a directly heated rectifier which has a substantial voltage drop. I'd expect to see 20-40 less volts with the NOS 5y3, maybe more. You can always change the cathode resistor to a slightly higher value when using the 5ar4 and allow the tubes to idle a little cooler but the tone of the output tubes changes slightly as plate voltage and current change.

FWIW, the modern Russian made Sovtek 5y3 is in truth a re-labeled Russian indirectly heated rectifier and will have far less voltage drop than a true 5y3. This has been a problem for many a builder but can be taken advantage of if you want to increase plate voltage in a 5y3 equipped amp.

jamie

[d. spree]

Thanks - when I built this amp the B+ was running a little hot, so I presume the AY3 would help address that? It may have been Bruce at Mission who suggested the swap to me (even though this is not one of his kits). I am not using russian tubes - the 5Y3s I have are US made GE and RCA tubes - I have a stash of about 8 of them.

[imaradiostar]

Bruce knows his stuff. As I've just proved in another thread you can't believe everything you hear on the internet so my advice is subject to verification by smarter people than myself.

It can't hurt to try it, especially if you've got spares. Personally I only have 2 or 3 5y3's in my whole stash of ancient tubes but I've ended up with a lot of 5u4's, 2 or 3 5ar4/gz34's and an assortment of other US made 5 volt indirectly heated rectifiers. It can be fun to try different tubes for different voltage drops. I tend to wire up my small 6 volt rectifier amps to take either an EZ81/6CA4 or a 6BW4 for the same reason- 6BW4 has a lot more voltage drop which can help with overly high plate voltages. The 6BW4 is also useful when you have a PT with plate voltages that are too high as it can take a higher peak input.

jamie

[Bruce / Mission Amps]

If you find the actual specs of the Russian 5Y3GT you'll note that it is much closer to a GZ30, 5Z4G or 5V4G... it isn't either of those tubes of course, but it is even further away from a NOS 5Y3GT!!
A NOS 5Y3GT is still very available on the NET and when used correctly in those amps built for a NOS 5Y3GT, the difference in price between the two doesn't justify using the Russian one.... well, in my opinion.
However, there is still a good reason to use a Russian 5Y3GT in other amps, especially those with an adjustable, fixed bias supply.
They work wonderfully in those amps.

[d. spree]

If you find the actual specs of the Russian 5Y3GT you'll note that it is much closer to a GZ30, 5Z4G or 5V4G... it isn't either of those tubes of course, but it is even further away from a NOS 5Y3GT!!
A NOS 5Y3GT is still very available on the NET and when used correctly in those amps built for a NOS 5Y3GT, the difference in price between the two doesn't justify using the Russian one.... well, in my opinion.
However, there is still a good reason to use a Russian 5Y3GT in other amps, especially those with an adjustable, fixed bias supply.
They work wonderfully in those amps.

Thanks Bruce - I do have a stash of US made 5Y3s - some GE and RCA tubes that I have collected and that cost me about $25 or so apiece. I do think (to me ears at least) that having replaced the stock kit GZ34 that came with the TubeDepot kit with an NOS US 5Y3 the amp sounds better - and the B+ dropped to within the range that is usually listed as desirable. What is the impact on the output tubes? I would imagine having the amp run too hot would generally tax the output tubes? I also presume that the B+ was originally a bit high was because of the TubeDepot power transformer - a blackface fender deluxe reverb PT. I guess having built 2 of these amps - the second being a Mission kit that came with a good NOS 5y3 - I am trying to understand the relationship between the various circuits and the relationships between the tubes - and how to get the best out of the tubes. Overall, I'm having fun with it all and wondering what to build next!!!