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Inspire by Dennis Had Enjoying Vacuum Tube Audio

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  #3711  
Old 05-14-2017, 10:16 AM
FloridaBoy FloridaBoy is offline
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The copper V-Caps will be a revelation. Be sure to re-visit your 6V6's after they settle in. Do you have a 5R4GY rectifier?
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  #3712  
Old 05-14-2017, 11:58 AM
Musica Amantem Musica Amantem is offline
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Originally Posted by FloridaBoy View Post
The copper V-Caps will be a revelation. Be sure to re-visit your 6V6's after they settle in. Do you have a 5R4GY rectifier?
No, I don't. That one features 67% higher max plate voltage (750 vs 450 volts) compared to my four preferred rectifiers, plus a higher voltage drop (except for the 80):

5U4-G - 5.0 - 3.0 - 44 - 225 - 450 - octal 5Z3 (274)
5AR4 - 5.0 - 1.9 - 17 - 250 - 450 - low Vdrop 5U4/5Y3
5Z4 - 5.0 - 2.0 - 20 - 125 - 350 - low drop 5Y3
80 - 5.0 - 2.0 - 60 - 125 - 350 - 4pin 5Y3

5R4-G/GY 5.0 - 2.0 - 67 - 250 - 750 - high voltage 5U4

Any technical concerns / risks with it?

Here's a quote from poster wyatt at another forum explaining the effects of these specs in an amp:

"The Vdrop is the voltage drop across the rectifier, those numbers (-17, -20, -44, -60) are over-simplified, the actual Vdrop will depend on the actual incoming AC voltage becing rectified. The 5AR4/GZ34 has the least Vdrop, then the 5Z4, then the 5U4G and finally the 80 (5Y3)."

"A side-effect of the voltage drop is the sag it adds. The more Vdrop, the less efficient the rectifier is, meaning it takes longer to supply the current. This adds Sag. When you pick a note or strike chord, the amp demands more current and the less efficient rectifiers can't supply it right away, so you're note/chord sort of drops in volume before ramping back up again. The more the amp is cranked the prominent the sag."

I adhere to these observations because I have always preferred the sound of low Vdrops in my rig. The goto 274B in my case is an intermediate Vdrop (44) so it's a tradeoff and it sounds great with smaller output tubes. The preferred 5AR4 is ideal with larger (more current demanding) output tubes (6550 / kT-88) and this rectifier limits sag.

"Higher voltages mean more headroom and tighter feel. Because the plate voltage changes, you should check bias after swapping rectifiers."

The last statement may create a problem since our amps are self-biased. Should this be a consideration?

Last edited by Musica Amantem; 05-14-2017 at 12:51 PM.
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  #3713  
Old 05-14-2017, 12:26 PM
FloridaBoy FloridaBoy is offline
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No concerns. I wonder what the voltage drop of the Sophia 274' is? I can't find the answer.
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  #3714  
Old 05-14-2017, 12:54 PM
Musica Amantem Musica Amantem is offline
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Originally Posted by FloridaBoy View Post
No concerns. I wonder what the voltage drop of the Sophia 274' is? I can't find the answer.
Its in my earlier post: 44 (middle-of-the-road). I edited that post and you can read the implications there again or here:

The goto 274B in my case is an intermediate Vdrop (44) so it's a tradeoff and it sounds great with smaller output tubes. The preferred 5AR4 is ideal with larger (more current demanding) output tubes (6550 / kT-88) and this rectifier limits the corresponding sag.

In addition, I remember Dennis saying the 5U4G (274) works better with 6V6 / 6L6 and the 5AR4 with 6550 / KT-88 relative to the 2nd order harmonics released near clipping.

Last edited by Musica Amantem; 05-14-2017 at 01:16 PM.
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  #3715  
Old 05-14-2017, 01:31 PM
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Beatlebum Beatlebum is offline
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Originally Posted by Beatlebum View Post
So I'd been reading up on power tubes and possible alternates to the GL KT66's in my Inspire Fire Bottle PSE. Not unhappy at all with the sound just wanting to learn more and seeing as I'm a huge fan of good 6L6 tubes I stumbled across some threads about the new Tung-Sol 7581A tubes.

Said what the heck and went ahead and ordered a quad of the 7581A's and I figured at $100 for the four of then, if they didn't work it wouldn't be the end of the end of the world.

These TS 7581A's are incredible sounding!

They have the best attributes of really good 6L6's (crystal clear, great highs, big soundstage) along with the bass and slam of the GL KT66's. The dynamics of these 7581A's are stunning!


Interestingly, the 7581A's sound better with a Brimar 6SL7 driver than my various NOS 6SN7's.

These 7581A's are even better sounding after some time on them. The dynamics are really good. Bass drums kicks have incredible impact.
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  #3716  
Old 05-14-2017, 02:46 PM
o o is offline
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A for sale ad says the amp can use 300B tubes?

Dennis Had Inspire KT88 tube amp. This amp will use KT88, EL34, 6L6, 6V6, and 300B power tubes. With 6V6 tubes it makes about 7 WPC. With the KT88 it makes 12WPC. Off white powder coat with faux wood front

Something in not adding up for me.
Any insight?

Thanks.
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  #3717  
Old 05-14-2017, 03:58 PM
FloridaBoy FloridaBoy is offline
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Quote:
Originally Posted by opnly bafld View Post
A for sale ad says the amp can use 300B tubes?

Dennis Had Inspire KT88 tube amp. This amp will use KT88, EL34, 6L6, 6V6, and 300B power tubes. With 6V6 tubes it makes about 7 WPC. With the KT88 it makes 12WPC. Off white powder coat with faux wood front

Something in not adding up for me.
Any insight?

Thanks.
The ad is incorrect.
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  #3718  
Old 05-14-2017, 03:59 PM
Musica Amantem Musica Amantem is offline
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Quote:
Originally Posted by opnly bafld View Post
A for sale ad says the amp can use 300B tubes?

Dennis Had Inspire KT88 tube amp. This amp will use KT88, EL34, 6L6, 6V6, and 300B power tubes. With 6V6 tubes it makes about 7 WPC. With the KT88 it makes 12WPC. Off white powder coat with faux wood front

Something in not adding up for me.
Any insight?

Thanks.
Most likely a mistake.

BTW, I came across a paper from Steve Deckert (Decware) which addresses differences between true triodes and pentodes strapped as triodes. Here's a quotation that called my attention:

"In a pentode such as the EL34 where the screens are not tied together internally, it is possible to wire it as a "true triode". It is the only pentode I know of that is. The other ones have internal connections on the screens that can't be changed so you end up with a "Pseudo triode" as I've heard it called."

In my Triode-strapped amp, the KT-77 sounds best. I know this tube is a far relative of the EL34 and its a tetrode, but makes me wonder if anyone has got a better result with the EL34 than with the KT-77 in his Triode-wired Inspire, OTBE. I remember someone mentioning a Mullard EL34, but I cannot tell if that poster had a Triode-wired Inspire amp. I guess the only way to find out is trying one ... There goes my determination to stop chasing down new tubes

Last edited by Musica Amantem; 05-14-2017 at 04:22 PM.
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  #3719  
Old 05-14-2017, 05:22 PM
o o is offline
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Amp was made on 9-30-13; seller claims "I once asked Dennis if I could put a tube in, I can't remember which, and he said stick it in. If it works, yes, if it doesn't, no." and "I have used the 300B output tubes, and have a set of Valve Art tubes to go with it."
I thought 300B requires totally different circuit/voltages.
Seller gives pentode power ratings for other tubes.
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  #3720  
Old 05-14-2017, 05:45 PM
FloridaBoy FloridaBoy is offline
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Quote:
Originally Posted by opnly bafld View Post
Amp was made on 9-30-13; seller claims "I once asked Dennis if I could put a tube in, I can't remember which, and he said stick it in. If it works, yes, if it doesn't, no." and "I have used the 300B output tubes, and have a set of Valve Art tubes to go with it."
I thought 300B requires totally different circuit/voltages.
Seller gives pentode power ratings for other tubes.
300B is a 4 pin tube and will not work in the amp.
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