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In Reply to: Re: Rectifier Flashing.... posted by Derick on September 07, 2002 at 13:26:12:
Derick, as Steve rightly points out, the 5V4 is NO sub for a 5U4G, and in a Sun amp, it pumps way too much current for a 5V4 to handle. The 5V4 is rated MUCH less than a 5U4. When you see arcing on startup, you are causing damage to the amp. Continued use of a 5V4 in this amp will cause power supply cap failure, and when they arc for the last time before blowing out, they may very well take the power tubes with them.You should never do this kind of thing, subbing a wrong tube in is almost always a disaster waiting to happen.
In the Sun amps, you can sub a 5AR4 (only a NOS one) for the 5U4G, this will reduce the headroom a little and raise the operating point of the power tubes. It is also ok to sub a 5R4, this will drop the operating point a bit and give a slightly more open sound.
The Mullard 6X4 flash at startup is typical of genuine Mullard tubes and is no issue.
Follow Ups:
Hi,Thanx for advice Robert, I was naive and stupid about the current draw, and ignored it as they both are rated at 5V. I'll just use the Russian 5U4G for the meanwhile instead I guess. The large base Mullard GZ34 seems to lack headroom when I want more volume alright. And thanx for the reassurance that the Mullard 6X4's flashing is normal. I hope the amp is fine though *fingers crossed*.
Yeah, the voltage drop on the GZ34 is much less than a 5U4G, so that'll drop the headroom a bit much.You can get some very good 5U4's for a reasonable price that will give you a big time better sound, look for Tungsol 5U4GB's - which are knock-out fantastic, also don't discount 1950's/early 60's GE 5U4GB's which are very good too, both can be found for a reasonable price.
Hi Robert,I've seen GE 5U4GB's which have a straight glass compared to the coke bottle type typical of 5U4G's. Are these the 50's-60's types you recommend? Maybe there are Bendix type 5U4's too....
No, there never was a Bendix 5U4 type made. Bendix tubes can be variable in sound anyways, some are good, others not so.There are GE 5U4GB's of every vintage imaginable. GB's are always straight glass. Don't get hung up on the fetish of believing the older coke bottle types are always superior, some are great - old Tungsol, Sylvania, for example, some are not so spectacular - the NU, KenRad come to mind. Some GB's are awful - later Sylvanias are one - but late 50's Tungsol, RCA or GE are very good.
There never was a good Euro 5U4 type, except the GEC U52 which is very good, and Mullard GZ series. There are some god-awful Euro types floating around with names like Ultron, etc. which are to be avoided.
I think your amp uses a single rectifier, if so, this is an advantage because singles pop up on Ebay all the time at good prices.
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