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Can you really get 100W out of 4 kt88's?

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Posted on March 1, 2015 at 10:00:50
lolek
Audiophile

Posts: 11
Joined: September 3, 2011
 I currently have an Audio Research VSI 55 that puts out about 50 watts with 4 kt120's (formerly 4 6550's). I am looking at the VAC 200phi which is rated at 100 watts with 4 kt88's. Does the VAC really have double the power of the VSI55? How does the VAC squeeze out 100 watts from 4 output tubes?
thanks in advance for the response,
Lolek

 

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Not as an OTL, posted on March 1, 2015 at 10:14:46
Craiger56
Audiophile

Posts: 5573
Location: San Jose CA
Joined: April 3, 2002
Contributor
  Since: December 29, 2003
 But with the right transformers in a push/pull circuit it's easy.

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 1, 2015 at 10:17:26
skriefal
Audiophile

Posts: 117
Location: SLC, Utah
Joined: June 29, 2007
 The VTA M-125 provides 125+ watts from four KT-88s or 6550s without over-driving the tubes.

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 1, 2015 at 10:52:18
BCR
Audiophile

Posts: 2446
Location: connecticut
Joined: April 7, 2009
 Check this!

 

or this, posted on March 1, 2015 at 11:31:26
Bill Way
Audiophile

Posts: 1884
Location: Toms River NJ
Joined: May 28, 2012
Contributor
  Since: December 14, 2012
 Manley 120 monoblocks put out 120W from a pair of KT90s. I get great tube life, but suspect that's because I normally run them at pretty low levels.

WW
"Put on your high heeled sneakers. Baby, we''re goin'' out tonight.

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 1, 2015 at 12:47:32
rws
Audiophile

Posts: 303
Location: Minnesota
Joined: September 7, 2004
 I friend of mine had a VAC amp that was 100wpc it was originally 80 but VAC offered a upgrade and he had the upgrade done.




"Sometime I will have to give account of myself. How would the Father in heaven judge me if I followed others and not Him", Anton Bruckner

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 1, 2015 at 12:52:06
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 Yes, in class B PP.

 

Sure, posted on March 1, 2015 at 14:18:01
E-Stat
Audiophile

Posts: 37643
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 VTL does it with the S-200 with each channel having four 6550Cs for 200 watts tetrode / 100 triode output.

 

Read the datasheet, posted on March 1, 2015 at 15:26:19
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 The datasheet for KT-88 valves specifies a class AB1 operating point that will deliver 100W with TWO tubes.

 

Roger Modjeski gets 125W from his RM-9 MkII nt, posted on March 1, 2015 at 15:29:53
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

And 35 wpc out of a pair of EL84s per side in the RM-10. /nt\, posted on March 1, 2015 at 20:12:47
Opus 33 1/3
Audiophile

Posts: 4184
Location: D.C. Area
Joined: February 19, 2014




Opus 33 1/3

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 2, 2015 at 05:36:38
Justlisten2
Audiophile

Posts: 1266
Location: SE PA
Joined: March 8, 2001
 I'm getting 85 wpc out of my VAC Sigma 160i integrated amp which uses 4 KT88's.

I see the VAC 200 Phi is heavier, so I'll assume bigger transformers. I'm sure Kevin can squeeze out another 15 wpc using bigger transformers.

 

Kinda doubt it, posted on March 2, 2015 at 11:53:04
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 I would be interested to see that measured.

A voltage doubler being used to power a class B amp is asking for trouble/bad performance. I once messed around with EL84's running in class B on a doubler power supply. They did well until cutoff, then the doubler sagged, power dropped like crazy, and distortion went way up. The normal practice to make a power supply with good regulation over a wide variety of currents is with a choke input filter, which is impossible on a doubler.

He also admits to removing the balancing resistors across electrolytic caps in series. This has caused pretty serious problems with some rather notorious production amplifiers.

 

E-mail Rodger Modjeski at Ram Labs. Maybe he can splain it., posted on March 2, 2015 at 13:29:34
Opus 33 1/3
Audiophile

Posts: 4184
Location: D.C. Area
Joined: February 19, 2014




Opus 33 1/3

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 2, 2015 at 13:57:08
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 I certainly hope so, (4) kt88's are a lot of juice!

 

RE: Can you really get 100W out of 4 kt88's?, posted on March 2, 2015 at 16:38:05
lolek
Audiophile

Posts: 11
Joined: September 3, 2011
 So, is the circuit topology for a 50 watt amplifier with 4 kt88's different than the circuit for a 100 watt amplifier with 4 kt88's? Is it a superior transformer that enables a greater amount of wattage from 4 output tubes? What are the advantages and disadvantages of using more output tubes for the same amount of wattage?
thanks for all the responses,
Lolek

 

RE: E-mail Rodger Modjeski at Ram Labs. Maybe he can splain it., posted on March 2, 2015 at 19:47:20
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 There's nothing to explain. A class B amplifier fed by a voltage doubler is just a terrible idea. I don't believe the output power claims are possible.

 

RE: E-mail Rodger Modjeski at Ram Labs. Maybe he can splain it., posted on March 4, 2015 at 15:10:48
1patrick
Audiophile

Posts: 3
Location: North Fla
Joined: March 4, 2015
 grasshopper have a lot to learn. it's a proven design since 1989

 

RE: E-mail Rodger Modjeski at Ram Labs. Maybe he can splain it., posted on March 4, 2015 at 18:31:13
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 Please do show me the measurements. I've actually tried building amps like that, and I understand why they don't work well.

 

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