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Discussion Starter · #1 ·
In the grand tradition of not letting well enough alone . . . LOL

Actually, I love my old tube rectified Traynor bassmasters but they are a little "stiff" and strident sometimes (the transient attach can be quite percussive). I was reading that swapping out the 5Ar4 rectifier can reduce the voltages on the amp and allow the amp to compress, break up, and "soften" so to speak. The problem is, I keep reading conflicting reports.

1.) One of the first things I looked at was a 5U4 but these draw 3amps and may stress the transformer (although the bassmaster's transformers are the size of my head!).

2.) The second tube I've been looking at is the 5R4. It seems like a safe bet as it also draws 2 amp but will bring down the voltages in my amp.

3.) The good ol' 5Y3. I never thought this would be possible, but apparently some guys are subbing them in! The added bonus of the 5Y3 is that I have a Sovetk 5Y3 sitting in my closet.

So whay say ye CGF? What is safe, what isn't? Feel free to directly contradict each other like the rest of the internet ! :)

TG


Rectifier comparison and interchangeability chart | KCA NOS Tubes & Amplifier Repair
 

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I can't even find a schematic for a YBA1 with a tube rectifier. Whats your B+ voltage and the bias current of the output tubes?
 

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That Sovtek 5Y3 doesn't have a voltage drop as real 5Y3, it's closer to 5AR4/GZ34.
I would try 5U4, measure 5V heater voltage, if it didn't drop and power transformer is not overheating you're good. I don't believe that extra 5Watts would stress hammond transformer.
 

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I agree with the guys above. I don't think the extra amp on the 5V circuit would stress that amp and do like epis said and measure the voltage drop to make sure it isn't significant, cause if it is then you probably are stressing it.

5Y3 in this amp would be right on the edge of its capabilities, but this wouldn't be the first time a tube was stressed out in a guitar amp. I like to use things as they are designed though. I am not about to throw a donut tire on my car and drive around at 110 kph just to see how far I can push it past its recommended ratings.
 

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I'd be wary of subbing a 5Y3 in there, especially if it's a newer issue tube (i.e. not something USA made NOS). With regard to the 5U4, I can't imagine a Traynor transformer of that vintage having any issues with such a substitution. Calling them "overbuilt" is a complete understatement IMO.
 

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Discussion Starter · #7 ·
Thanks so much guys. I should mention that the amp runs 7027s (rather the EL 34s) but I sometimes use 6L6s.

Between the 5u4 and 5R4, is there any reason to choose a 5u4 over the 5R4 given that the 5U4's slightly out of spec (although I am doubting it would damage these transformers.)

If I were to go to a 5Y3, I would also switch the power tubes to JJ 6V6s and up the load to 16 ohms. In fact, I may go to 6V6s regardless of what rectifier I end up using.

Thanks again, just trying to weight all my options before adding tubes to my cart! :)
 

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I don't know if you are aware that there is more to it than just putting 6V6's in there. You'll want to check the bias to make sure the tubes aren't drawing to much current as well as put a 16 ohm load on the 8 or 4 ohm tap to cause the reflected primary impedance to double or quadruple to minimize dynamic current draw as well. Then you need to make sure the reduction in operating current hasn't caused the B+ voltage to raise to high, being bad for the 6V6's as well as the inverse voltage rating of the rectifier.

There might be a few other things I missed.
 

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Discussion Starter · #9 ·
Yes, thanks dcole. Some previous discussion of the 6v6s is here.

I'll probably start with a rectifier swap before considering the 6v6s.



I don't know if you are aware that there is more to it than just putting 6V6's in there. You'll want to check the bias to make sure the tubes aren't drawing to much current as well as put a 16 ohm load on the 8 or 4 ohm tap to cause the reflected primary impedance to double or quadruple to minimize dynamic current draw as well. Then you need to make sure the reduction in operating current hasn't caused the B+ voltage to raise to high, being bad for the 6V6's as well as the inverse voltage rating of the rectifier.

There might be a few other things I missed.
 

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Here's another handy chart that shows the voltage drop & other specs for various rectifier tubes (not just 5Y3's)
 

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Discussion Starter · #13 ·
Here's another handy chart that shows the voltage drop & other specs for various rectifier tubes (not just 5Y3's)
Thanks for this. To my distinctly non-techy eyes, it seems the 5R4 is the best choice as it is very similar to the 5AR4 outside of a large voltage drop. Is there any point in trying a 5Y3? What would be the "advantage" of running a 5Y3?

TG
 

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One thing you are forgetting is the maximum capacitance you can put directly after the rectifier. Maximum for a 5ar4 is 60ufd. The maximum for a 5r4 is 4ufd.
What happens is the tube can only supply so much current to charge the capacitor. The bigger the cap, the more current.
The 5r4 will work but its lifespan will be greatly shortened if too large a cap is used.
What is the value of the first cap after the rectifier?
 

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Discussion Starter · #15 ·
I actually have a copy of the old Yorkville service docs for converting the tube rectified units to SS. Here is a hand drawn schematic of the tube rectifier circuit that is included in these docs. Perhaps it can answer a few of the more technical questions posed in this thread.

 

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Discussion Starter · #17 ·
Now I see why Traynor was converting to solid state rectifiers. There's even too much capacitance for the 5AR4 (although not by much). That 80ufd is 20 times higher than the 5R4 should see. Personally, I would stick with the 5AR4.
Aw man, after all of that!

Seriously though, thanks so much for the info. I guess I will just stick with stock tube if I risk causing damage.

Thanks again,
TG
 
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