From mgarvi–(at)– Tue Dec 12 11:50:15 CST 1995
Article: 4218 of
From: mgarvi–(at)– (Mark Garvin)
Subject: Re: Need 5AR4 data
Date: 11 Dec 1995 22:52:39 -0500
Organization: PANIX Public Access Internet and Unix, NYC
Lines: 40
Message-ID: <4aiua7$gl--(at)>
References: <49kt0o$s5--(at)> <4a33ad$9b--(at)> <4a4i4b$5m--(at)> <4a5e78$n0--(at)> <4af4at$ce--(at)> <4ahn2d$1m--(at)>

>: In <4a5e78$n0--(at)> kurt–(at)– (Kurt Strain) writes:

>: >: A 5U4, on the other hand, has less rectifier resistance, about 50 ohms.
>: >: It might be better to use the 375 Vrms transformer for it. Anybody using
>: >: 5U4’s to replace 5AR4 should expect higher DC voltages in capacitor input
>: >: supplies.

>: Mark Garvin (mgarvi–(at)– wrote:
>: Hi Kurt, In comparing a 5U4 to 5AR4, I’ve found that the 5U4 drops
>: considerably MORE voltage than the 5AR4.

>In <4ahn2d$1m--(at)> kurt–(at)– (Kurt Strain) writes:

>Then either the 5U4 datasheet is wrong in stating their plate impedance
>or the 5AR4 is not 160 ohms plate resistance. Could someone please double
>check? I’m talking about the conditions for 420VDC, 170mA operation, and
>they need to be apples to apples comparison. Only plate impedance at
>given voltage and current effects the output for a given input capacitor.

Hi Kurt, I guess the least I can do after all the time you’ve taken on
your posts is to run this down for you. I’ve checked this on the nearest
amp with a rectifier: a Fender Vibrolux. Sorry, no single-ended triodes
on the bench. First cap is 30 uf.

B+ with no load Under load
—————– ————
Silicon rect480 volts 445 v
5AR4 (Mullard) 475 426
5U4 (RCA) 469 404

I’ve checked other good 5AR4’s such as Amperex, but many of these are
probably rebranded Mullards anyway. The Sovteks perform in similar
fashion, but with an occasional fireworks show. Others have had better
luck with the Sovteks than I.

The numbers above are pretty consistent with my past experience.

Anyone disagree?

Mark Garvin

From morga–(at)– Tue Dec 12 11:50:37 CST 1995
Article: 4239 of
From: Roy Morgan
Subject: Re: Need 5AR4 data
Date: 12 Dec 1995 17:19:27 GMT
Organization: National Institute of Standards and Technology
Lines: 18
Message-ID: <4akdiv$ni--(at)>
References: <49kt0o$s5--(at)> <4a33ad$9b--(at)> <4a4i4b$5m--(at)> <4a5e78$n0--(at)> <4af4at$ce--(at)> <4ahn2d$1m--(at)>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 1.2N (Windows; I; 16bit)
To: kurt–(at)–

Do not confuse dynamic plate resistance with basic voltage drop.

The 5AR4’s “plate resistance” is the ratio of SMALL voltage changes due to
SMALL current changes at some specified base current.

The “higher voltage drop” mentioned by one poster is the difference in steady
state dc filter output comparing the two tubes.

Not the same.

— Roy Morgan / Nist North / Building 820 – Room 562 / Gaithersburg MD 20899
(National Institute of Standards and Technology, formerly NBS)
301-975-3254 Fax: 301-948-6213 Internet: morga–(at)–


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