Dual rectifier tubes?

General Tech Discussion - Anything amp-ish goes!

Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

Post Reply
User avatar
yello
Occasional poster
Occasional poster
Posts: 212
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Dual rectifier tubes?

Post by yello »

I have a PP 6AQ5 amp that runs dual rectifier tubes, both 6x4. I love it, and have always been curios why there are two rectifiers. In this amp it looks like each 6x4 rectifier is fed by a different side of the PT, then the outputs are bridged.

Image

There is also a parallel single-ended 5F2a type amp called the Angela Super Single-Ended that I want to build, that uses two 5y3's along with two 6v6's in parallel. In this amp the 2nd 5y3 is wired to the same pins as the first.

Image

Generally speaking, what is the purpose of having two rectifiers tubes - to lower the B+ voltage? Other benefits? Different ways to wire them together like above, and why?

Ultimately, I'm wondering if adding a second 5y3 to a vintage 5e3 type amp that already has an extra octal socket in the right place is a helpful way to lower the voltage that is now too high because of modern 123v at my outlet, in lieu of or in addition to other methods of lowering the B+ like zener diode, or resistors (currently uses an adjustable 10w 500r resistor).
0 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 212
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Dual rectifier tubes?

Post by yello »

Related to the above question (would still love some insight if anyone has any), how do I figure out current draw to ensure a PT offers enough for a tube layout?

I want to build a variant of the above "Angela Super Single Ended" amp. The stock amp I will mod has one 12ax7, one 6aq5, and one 6x4. I want to add another 6aq5 to be parallel single ended, and add another 6x4 to have dual rectifiers.

All the current draw calculators/calculations I find online do not reference 6x4 or 6aq5, so not sure how to figure out if my PT can handle the current duty of this fun little project.

The PT is a Stancor PM8418, 230-0-230, 50ma DC, 6.3v @ 2.5A.
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 3955
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Dual rectifier tubes?

Post by JMPGuitars »

yello wrote:
Tue 03/21/23 1:23 pm
All the current draw calculators/calculations I find online do not reference 6x4 or 6aq5, so not sure how to figure out if my PT can handle the current duty of this fun little project.
The easiest way to figure that out is to look at the tube datasheets and see what the current draw is for each. Then add them together. You could also look for tube equivalents to see how they compare. 6aq5 is supposed to be similar to 6v6, but I don't know if they're exact. Check the datasheets.

Thanks,
Josh
1 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright

Modern Ground Schemes
Soldering Technique
B+ Voltage Reduction
Amplifier Tools & Parts Info


Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

Re: Dual rectifier tubes?

Post by TriodeLuvr »

The two rectifier tubes in the first schematic are undoubtedly being used that way in order to increase the current capability. Incidentally, the 6X4 and 6X5 (octal equivalent) are both known for developing heater-cathode shorts. I wouldn't build with either tube type unless a separate filament winding is available that can be left floating. Akai recognized this issue way back in the '60s, and all the M6, M7 and M8 reel decks used a separate winding for the 6X4.

Jack
3 x

Daviedawg
Superior Amp Tech
Superior Amp Tech
Posts: 748
Joined: Fri 01/08/10 2:00 am
Location: Scotland

Re: Dual rectifier tubes?

Post by Daviedawg »

A small number of my lower output SE amps have been fitted with 6X4 rectifiers some of them ten years ago. I was not aware of any issue with them and they are fed by single filament supplies beside the 6AQ5s.
Thanks for the warning Jack. No plans to build any more at the moment and I will check with the users to see if any issues have arisen. I have suitable transformers if repairs are needed.
Dd
2 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 212
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Dual rectifier tubes?

Post by yello »

TriodeLuvr wrote:
Tue 03/21/23 5:13 pm
The two rectifier tubes in the first schematic are undoubtedly being used that way in order to increase the current capability. Incidentally, the 6X4 and 6X5 (octal equivalent) are both known for developing heater-cathode shorts. I wouldn't build with either tube type unless a separate filament winding is available that can be left floating. Akai recognized this issue way back in the '60s, and all the M6, M7 and M8 reel decks used a separate winding for the 6X4.

Jack
Interesting info Jack, I have lots of 6x4 amps (all running 6aq5 power tubes) and have never experienced a problem, and most of them are run quite hard.
0 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 212
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Dual rectifier tubes?

Post by yello »

JMPGuitars wrote:
Tue 03/21/23 3:45 pm
yello wrote:
Tue 03/21/23 1:23 pm
All the current draw calculators/calculations I find online do not reference 6x4 or 6aq5, so not sure how to figure out if my PT can handle the current duty of this fun little project.
The easiest way to figure that out is to look at the tube datasheets and see what the current draw is for each. Then add them together. You could also look for tube equivalents to see how they compare. 6aq5 is supposed to be similar to 6v6, but I don't know if they're exact. Check the datasheets.

Thanks,
Josh
I though about referencing tube datasheets, but I'm not sure where to look on them to start to calculate things correctly.

https://frank.pocnet.net/sheets/127/6/6X4.pdf

https://frank.pocnet.net/sheets/127/6/6AQ5.pdf

https://frank.pocnet.net/sheets/049/1/12AX7A.pdf
0 x

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

Re: Dual rectifier tubes?

Post by TriodeLuvr »

"The PT is a Stancor PM8418, 230-0-230, 50ma DC, 6.3v @ 2.5A."

The schematic you posted shows HV of +285 and cathodes at +17. I can't tell the exact anode voltage, but it's clear the tubes are running with about +270V across them.

The 6AQ5 datasheet indicates that a pair of 6AQ5 operating in push-pull AB1 under similar conditions (+250V anodes/-15V grids) will draw 75mA for the anodes and screens. That's at idle. They will draw more than 90mA at full output. This is all beyond the ratings of the transformer.

Jack
1 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 212
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Dual rectifier tubes?

Post by yello »

TriodeLuvr wrote:
Thu 03/23/23 5:04 pm
"The PT is a Stancor PM8418, 230-0-230, 50ma DC, 6.3v @ 2.5A."

The schematic you posted shows HV of +285 and cathodes at +17. I can't tell the exact anode voltage, but it's clear the tubes are running with about +270V across them.

The 6AQ5 datasheet indicates that a pair of 6AQ5 operating in push-pull AB1 under similar conditions (+250V anodes/-15V grids) will draw 75mA for the anodes and screens. That's at idle. They will draw more than 90mA at full output. This is all beyond the ratings of the transformer.

Jack
Hi Jack,

The Schematic in the first posting about the military amp, asking about its dual 6x4 rectifiers as an example for my dual rectifier question, is a different amp and schematic than uses the prposed Stancor, sorry if stacking my two posts made it confusing.

The amp with the Stancor is a Moviola amp, seen here, schematic in bank of photos:

https://tylergilroy.weebly.com/vacuum-t ... fiers.html

I want to add another 6x6 and another 6aq5. Thus trying to calculate if possible for either/both.

The
0 x

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

Re: Dual rectifier tubes?

Post by TriodeLuvr »

I'm not sure how you would add a second 6AQ5, but the transformer you described isn't rated to power two in either parallel or push-pull. You'll need more B+ current for that. I would also recommend a 6CA4 (or appropriate 5V rectifier) rather than two 6X4s, especially if the transformer doesn't have a separate filament winding.

Jack
2 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 212
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Dual rectifier tubes?

Post by yello »

TriodeLuvr wrote:
Sat 03/25/23 5:58 pm
I'm not sure how you would add a second 6AQ5, but the transformer you described isn't rated to power two in either parallel or push-pull. You'll need more B+ current for that. I would also recommend a 6CA4 (or appropriate 5V rectifier) rather than two 6X4s, especially if the transformer doesn't have a separate filament winding.

Jack
Thanks Jack, appreciate your insight. Is it because it only supplies 50ma DC? Would a 100ma PT work for adding a second 6aq5. And is there enough current for two 6x4? What drove the alternate recommendation for rectifiers?

I'm trying understand the above so I can apply the principle to other amps, and expand my understanding in general of how to calculate.
0 x

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

Re: Dual rectifier tubes?

Post by TriodeLuvr »

Yes, a transformer rated for 100mA DC would be sufficient. The 6AQ5 datasheets state the current draw for a single tube in Class A as well as a pair in push-pull. 250V B+ is generally the maximum for good life with this tube type. I wouldn't use two rectifier tubes if one of a different type can do the job.
1 x

Post Reply