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March 08, 2021, 01:13:39 PM

Author Topic: Rolling tubes  (Read 418 times)

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Offline patrick620

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Rolling tubes
« on: December 29, 2020, 04:55:16 PM »
Has anyone rolled any other tubes with the same pin out as a 6v6? Is the PT up for it?
« Last Edit: December 29, 2020, 05:00:20 PM by patrick620 »

Offline Paul Joppa

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Re: Rolling tubes
« Reply #1 on: December 29, 2020, 06:39:21 PM »
Here's what I have found on the web.  Update January 2, 2021

Strict 6V6 equivalents should be OK:

5871 - made for mobile (high vibration) operation, no interface resistance means high-purity cathode

7408 - specifically for audio; "controlled zero-bias characteristic"

Different heater currents up to 0.75 amps should be OK with AC heating, but the dropping resistors must be changed, and when the DC heater upgrade is available, it will not tolerate more than 0.45 amps:

6K6 - 0.4A heater so may need slight change in dropping resistors

5992 - Red Bank super reliable but 0.6 amps. Data sheet curves look less linear than regular 6V6's.

EL84 might work, with a 9-pin adapter if there is one, plus a change in bias resistor. I have not looked into it yet. High heater current, AC heating only

6L6 and EL34 need too much heater current even if AC heated


9-pin (needs adapter) There are five but they ALL have different pinouts!

6CM6 is an exact equivalent - 9CK socket

6BW6 is an exact equivalent - 9AM  socket (pin 1 internal connection, pin 6 N/C)

6061 is an exact equivalent - 9AM socket (pin 1 N/C, pin 6 internal connection) - rugged/reliable

6973 is an updated version, with slightly different specs - 9EU socket (n.b. identical to 6CZ5 but specified for audio)

6CZ5 is an updated version, with slightly different specs - 9HN socket (n.b. identical to 6973 but specified for TV vertical output)


7-pin (needs adapter):

6AQ5 - same as 6V6 but 250v max (OK for Moreplay)

6005 - GE 5-star industrial rugged, reliable

6095 - same as 6AQ5

6669 - for car radios; tolerates varying heater voltage better

6928 - Very rare, very expensive; rugged, reliable, long-life, more linear than others


« Last Edit: January 02, 2021, 07:01:20 PM by Paul Joppa »
Paul Joppa

Offline patrick620

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Re: Rolling tubes
« Reply #2 on: December 29, 2020, 10:26:59 PM »
Good info. Thanks. Using a 6v6 as a preamp tube is uncharted waters for me. In a lower voltage preamp application I am guessing the tubes are running a bit cold. Makes me curious as to any advantage over a 12a** type preamp tube. Maybe less microphonic, more stable and rugged? I know that it can be done but why? I have been dealing with tubes for about 25 years and I love to learn new things.
« Last Edit: December 29, 2020, 10:48:19 PM by patrick620 »

Offline Paul Joppa

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Re: Rolling tubes
« Reply #3 on: December 30, 2020, 05:45:30 AM »
The main reason is to get a low output impedance without using feedback or transformers. The 6V6, wired as a triode, is more linear than most pentodes, and widely available/inexpensive, so we chose it for this preamp.

It also helps that its heater power requirement is fairly low so we can use a smaller power transformer to reduce cost.
Paul Joppa

Offline Paul Birkeland

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Re: Rolling tubes
« Reply #4 on: December 30, 2020, 05:56:47 AM »
Makes me curious as to any advantage over a 12a** type preamp tube.
Another advantage is a far more reasonable amount of gain. 
Paul "PB" Birkeland

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Offline 2wo

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Re: Rolling tubes
« Reply #5 on: December 30, 2020, 05:55:46 PM »
My first thought was 6Y6,but it draws way too much heater current...John
John Scanlon

Offline Paul Joppa

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Re: Rolling tubes
« Reply #6 on: January 02, 2021, 07:05:35 PM »
I have updated the list in Post 2 to clarify and add some 9-pin equivalents.
Paul Joppa