Carver Crimson 275 Measurements

[paulbottlehead]

Here's a link to some photos of the Carverfest 275 amp build:

https://thecarversite.com/topic/17761-carverfest-2018-tube-amp-build-picture-gallery/?tab=comments#comment-181112

Can you post some of those here? That website doesn't allow viewing without an account.

 

[Jazzman53]

There are many more photos on the Carversite forum. Here are a few:

 

[MakeMineVinyl]

Those photos seem to verify the 15 watt output transformer. Why did it get rated at 75 watts? Was anything mentioned about the output wattage capability at this meeting?

The output transformers on my Dynaco SCA-35 15 watt amplifier are a little bit bigger than the ones here. Very strange. I would have just rated the Carver amp at 15 watts per channel and called it good. Better still, dump the expensive KT120s, use EL84s, and use the money saved from the tube swap for a better output transformer.

The output transformers on my Audio Research D-76A amp (below - but not my amp) are huge by comparison, but it will put out an honest 75 watts.

 

[Jazzman53]

I have no clue about that. I vaguely recall a posting inquiring about the voltage fed to that little transformer. Also; I believe Greg Garska (of Nelion Audio) actually measured the amp's output-- I'm still looking for those posts.

 

[Zackthedog]

Hi all,

I attended the 2018 Carverfest and witnessed the 275 amp builds. Many (probably most) of the builders had never built an amp before and some mistakes were made, as some of them needed a bit of rework to get them up and running. Many parts were shipped directly to the Carverfest location in Bryson City, and I vaguely recall issues with some parts not arriving on time. In any case; I know that some amps were not completed during the festival.

I didn't buy a kit myself but I'm pretty handy so I pitched in and helped populate some of the boards, even though I had very little experience with electronics.

Anyway; I just wanted to confirm Jim Clark's posting about there being at least 60 non-factory-built 275's around. And I also witnessed Bob signing many of those DIY kit amps, even some that were not fully assembled at the time.

Here's a link to some photos of the Carverfest 275 amp build:

https://thecarversite.com/topic/17761-carverfest-2018-tube-amp-build-picture-gallery/?tab=comments#comment-181112

Well, kudos to you for offering to help out. This must have been a thrill for those involved--to actually build a tube amp of their own! And I don't mean that sarcastically, not at all.

And (again, not to slight your efforts by any means) this was a brilliant marketing ploy.

However...I have to wonder how, in the end, this will reflect on Bob if the product fails to measure up to the advertised specs.

Sure, Heathkit, Dynaco, Stancor, Peerless and other tube amp designers of yore offered kits that could be built at home. But, if properly constructed, the results would be in line with what they advertised. It will be interesting to see how a production Carver 275 amp measures.

 

[Jazzman53]

Yes; I wonder too. Bob certainly knows how to hype a product but it seems out of character for him pull an outright scam. I will be relieved if this turns out to be some kind of mistake.

 

[JeffGB]

It is sufficiently unbelievable, I wonder about whether these are even genuine Carver product and not some Chinese counterfeits (or USA for that matter).

I wondered the same but then I read his specifications. 19lbs is a correct weight for such puny output transformers. I had a HK Citation 1 back in the day that was rated a bit better but not much and it weighted approx 60lbs. Those output transformers will never produce a clean 75w at 20hz. That specification is fantasy (fraud?). There is NO tube amp that I am aware of that has output transformers that small and produces clean power at low frequencies.

When I was a kid output transformers like this showed up in Sears/Roebuck "hifi". Amplifiers with ratings like the Carver were the REASON the FTC rules were devised. They were considered a ripoff.

 

[Zackthedog]

The idea is not to rate the output transformer at 75 watts, but to use a small, specially wound transformer, with high-permeability core materials, to reduce weight but achieve good performance. The amp circuit has numerous compensation networks and runs the output tubes at very low current to make this work. I assume that was the theory, anyway. For example, Heathkit used a specially wound Peerless 16309 transformer in the original W5 kit amplifier. It was small and lightweight but it had nickel intermixed in the lams to increase the primary inductance and hence the low-frequency response. They were actually wonderful transformers, and did the job admirably, but they were only rated for 30 watts. This seems to be taking the idea too far.

 

[Zackthedog]

...but hey, don't take my word for it! According to Frank Malitz:

New Bob Carver Crimson 275 Stereo Vacuum Tube Amplifier-Taking orders.$2495 Shipped. Made in USA.

Jimclarkstereo.com . Demonstration available North of Rockford, IL.. (815) 323 0898. Bob Carver sound for just $2,495! Seventy five watts per channel at a price that will drive the competition into feedback mode. Bob and his staff are working hard to birth this new product. We didn’t achieve...

audiokarma.org

"Here’s Bob Carver experimenting with the winding in case you thought that was hyperbole."



Now whatever that is he's winding, it ain't no output transformer. For Pete's sake...

 

[Blumlein 88]

...but hey, don't take my word for it! According to Frank Malitz:

New Bob Carver Crimson 275 Stereo Vacuum Tube Amplifier-Taking orders.$2495 Shipped. Made in USA.

Jimclarkstereo.com . Demonstration available North of Rockford, IL.. (815) 323 0898. Bob Carver sound for just $2,495! Seventy five watts per channel at a price that will drive the competition into feedback mode. Bob and his staff are working hard to birth this new product. We didn’t achieve...

audiokarma.org

"Here’s Bob Carver experimenting with the winding in case you thought that was hyperbole."

View attachment 175043

Now whatever that is he's winding, it ain't no output transformer. For Pete's sake...

Crossover coil.

 

[Zackthedog]

Crossover coil.

That's what it looks like, yes.

 

[paulbottlehead]

The idea is not to rate the output transformer at 75 watts, but to use a small, specially wound transformer, with high-permeability core materials, to reduce weight but achieve good performance. The amp circuit has numerous compensation networks and runs the output tubes at very low current to make this work. I assume that was the theory, anyway. For example, Heathkit used a specially wound Peerless 16309 transformer in the original W5 kit amplifier. It was small and lightweight but it had nickel intermixed in the lams to increase the primary inductance and hence the low-frequency response. They were actually wonderful transformers, and did the job admirably, but they were only rated for 30 watts. This seems to be taking the idea too far.

High permeability doesn't mean higher power handling, and actually and the end of the day higher permeability can trade away power handling! Also if you look at some data points like transformers in the Monolith Magnetics catalog, inductance drops slightly for some of these higher permeability materials relative to the simple GOS laminated transformers that are otherwise identical.

This is a good depiction from Hitachi for their Finemet materials product literature. Saturation flux density is what one would be after to squeeze as much power as possible out of a small transformer. High permeability materials are more frequently used at low levels where core sizes are smaller and saturation is not so likely.

Compensation networks are generally aimed at stability.

The 16309 is an odd choice to bring into this conversation since they have a reputation for being undersized and failing, and Heathkit replaced them with a bigger part later.

 

[Zackthedog]

High permeability doesn't mean higher power handling, and actually and the end of the day higher permeability can trade away power handling! Also if you look at some data points like transformers in the Monolith Magnetics catalog, inductance drops slightly for some of these higher permeability materials relative to the simple GOS laminated transformers that are otherwise identical.

This is a good depiction from Hitachi for their Finemet materials. Saturation flux density is what one would be after to squeeze as much power as possible out of a small transformer. High permeability materials are more frequently used at low levels where core sizes are smaller and saturation is not so likely.

Compensation networks are generally aimed at stability.

The 16309 is an odd choice to bring into this conversation since they have a reputation for being undersized and failing, and Heathkit replaced them with a bigger part later.

Thanks for the correction, Paul. I was just trying to think through the logic of the choices made here, and I'd like to think that there *was* some logic involved, at least at some point.

I brought up the 16309 as an example of maintaining performance (or at least attempting to) in a reduced package size. It's true that a lot of them failed, but so did the power transformers in the W5. Heathkit's solution was a beefier output tranny and a thermistor to reduce the turn-on surge. I've also seen evidence suggesting that imperfect potting in the 16309s led to corrosion in the windings. But I have several working examples and in my experience they hold up if you treat them a little more gently than Heathkit did.

 

[paulbottlehead]

Yeah I have a local friend with a pair of W5s with the 16309s and he isn't quite sure what to do with them! I heard that those power transformers were produced for a huge order for a different customer, but that customer backed out and Heathkit offered to purchase them at a substantial discount. The 5R4 was likely a design choice to knock down B+, but I might opt for a 5AR4 to slow the warm up way down and use a small choke between the rectifier and first cap.

 

[Zackthedog]

Yeah I have a local friend with a pair of W5s with the 16309s and he isn't quite sure what to do with them! I heard that those power transformers were produced for a huge order for a different customer, but that customer backed out and Heathkit offered to purchase them at a substantial discount. The 5R4 was likely a design choice to knock down B+, but I might opt for a 5AR4 to slow the warm up way down and use a small choke between the rectifier and first cap.

Interesting, I've never heard that before. The GZ34 was only introduced the year before, and the previously-employed 5V4 wouldn't handle the higher voltages, so I just assumed they designed it around commonly available tubes.

Installing a thermistor and uprating the coupling cap voltage tolerances can help--power supply caps, too. There's a nice big space under the power tranny that can accommodate a board of fresh PS capacitors. Sheldon Stokes used to sell a PCB for this.

Over at Audiokarma, Dave Gillespie suggested that one culprit might have been the *turn-off* surge, the thump that can occur when the amps are turned off and can send a huge power spike through the outputs. In his thread "Regilding the Gilded Lily," on restoring a Heathkit W2, which suffered from the problem due to LF instability, he designed a small relay to avoid it. Might be worth looking at.

See comment #8:

Regilding the Gilded Lily: Heath's W-2M

INTRODUCTION Immediately following WW II, there was very little in the way of truly high fidelity amplification equipment available to audio enthusiasts. But then came D.T.N. Williamson's Landmark design that introduced the Williamson amplifier to the world in the May, 1947 edition of Wireless...

audiokarma.org

 

[mhardy6647]

boys, boys, boys! ... Carver... we're talkin' Carver here...


Speakin' of which -- id est the titular Crimson 275...
I was thinking about the specs. It struck me that there's an interestingly omitted word/concept in the power spec.

I don't see the word continuous in that spec, nor the notion that it's a continuous rating. We infer that the rated power capability is "continuous", and it's certainly implied -- but it's just as certainly not stated.

I am left to wonder whether we're looking at some sort of latter-day invoking of the old "music power" idea (which was even part of an IHF standard often observed in ads and catalogs back in the pre-FTC '74 days).

This would leave the amp out of compliance with the FTC regulations (and I am, truth be told, not at all clear of the state of those regulations in 2021 anyway) but could, it seems to me, eliminate any evidence of fraud with respect to the published specs.

 

[MakeMineVinyl]

boys, boys, boys! ... Carver... we're talkin' Carver here...


Speakin' of which -- id est the titular Crimson 275...
I was thinking about the specs. It struck me that there's an interestingly omitted word/concept in the power spec.

View attachment 175165

I don't see the word continuous in that spec, nor the notion that it's a continuous rating. We infer that the rated power capability is "continuous", and it's certainly implied -- but it's just as certainly not stated.

I am left to wonder whether we're looking at some sort of latter-day invoking of the old "music power" idea (which was even part of an IHF standard often observed in ads and catalogs back in the pre-FTC '74 days).

This would leave the amp out of compliance with the FTC regulations (and I am, truth be told, not at all clear of the state of those regulations in 2021 anyway) but could, it seems to me, eliminate any evidence of fraud with respect to the published specs.

That's certainly possible, and I'd like to see transient power tested on the 'store bought' amp. I'm uncertain the FTC regulations are even a thing these days.

 

[mhardy6647]

That's certainly possible, and I'd like to see transient power tested on the 'store bought' amp. I'm uncertain the FTC regulations are even a thing these days.

Ditto. This is all I've got:

The FTC may consider dropping the Amplifier Rule.

The FTC has recently announced reviewing its current rule, formally known as: “FTC Trade Regulation Rule Relating to Power Output Claims for Amplifiers Utilized in Home Entertainment Products”, or simply as the “Amplifier Rule”. The FTC reviews its rules every ten years, and it’s that time again...

www.audiosciencereview.com

I do "know" (i.e., I think I remember) that it has been changed (softened a bit) since the original regs of 1974. Specifically, I think that the preconditioning spec (what was it originally? 1/2 hour at 1/3 power, IIRC) which was very hard on an amplifier, has been altered to be less of a torture test than the original.

 

[egellings]

I'd take that big Carver amp (had I been duped into buying one) and rip those little output walnuts off it and put some real iron on there. Of course, if the power xfmr is also a walnut, then I'd have to edit that position as well.

 

[Ken1951]

Those photos seem to verify the 15 watt output transformer. Why did it get rated at 75 watts? Was anything mentioned about the output wattage capability at this meeting?

The output transformers on my Dynaco SCA-35 15 watt amplifier are a little bit bigger than the ones here. Very strange. I would have just rated the Carver amp at 15 watts per channel and called it good. Better still, dump the expensive KT120s, use EL84s, and use the money saved from the tube swap for a better output transformer.

The output transformers on my Audio Research D-76A amp (below - but not my amp) are huge by comparison, but it will put out an honest 75 watts.

View attachment 175039

Totally OT, but we sold those amps and I really loved them. Particularly driving the mids/highs on Tympani 1s.