Comparing and contrasting EL84 PP Integrateds

[specialidiot]

There are a lot of EL84/6BQ5 in push-pull integrated amps out there....

I've had the Dynaco SCA-35, an Eico HF-81, and now a Grommes 28PG.

The Dynaco was pretty nice, especially after the power mods. Jay had my HF-81 signing sweetly, especially the phono stage but its back in his shop for a touch up. And now I have the Grommes.

There are quite a few others, right? Heathkits come to mind, and there's an Olsen on BT right now.

Which of these amps are doing it right? Are there any stinkers?

 

[GordonW]

Stromberg ASR333 and ASR433 are big-time performers, IMHO. The amp circuit is especially good. My best home-build integrated amp was based on the output amp section of this, with a 6CG7 preamp (like the original, just stripped-down with a lower gain input tube and no tone controls).

Pilot SM245 may be the best of all, IMHO, comparing units in stock form...

Regards,
Gordon.

 

[buglegirl]

Hiya,

What about the Scott 299-B or even the 299-A. I would put these up against most anything.

There are also the Fisher Variants but I have not restored mine yet so no comment.

Although I do regret letting my ASR-433 go but can't have everything right ???

Frannie

 

[GordonW]

The Pilot just has better dynamic range than the Scotts, IMHO (the 222 and the early 299s)...

The Fisher 600 was OK... a bit noisy, IIRC, but sounded good.

Regards,
Gordon.

 

[buglegirl]

Hiya,

Yah I figured the Pilots are something special. Just not able to ever come close to acquiring one as they go for what I call insane money.

I have a Pilot 602 receiver which I guess should sound good once I get around to working on it.

Not sure how different it is from the SM245 though.

Frannie

 

[Redboy]

Frannie, one significant difference between those two Pilots is the output iron - the SM245 has much bigger transformers. You'll see opinions and claims "out there" that the transformers in the 245 are the same as those used in the venerable SA232, but according to the SAMS folders for the two amps, they are different and they have different primary impedances. Still, they're about the same size and probably sound every bit as good.

Your 602 has smaller output transformers, but they're still Pilot transformers and they will sound very nice indeed. :yes:

 

[PR Audio]

I had a Heathkit SA-2, great sounding amp in stock form, even better when I started modding it. The transformers on these SA-2's are highly sought after. When I sold it it had TAD EL84-STR's installed. Great amp and tube.

 

[Dmannnnn]

Have you considered running any of these amps as triodes? I am seriously considering it for one of the HF81's. I'm wondering if I can get some of that SET magic I experienced with the 300B.

 

[tiga]

Just curious - how would the amp section of my Pilot 110 integrated compare to these? Thanks.

Frannie, one significant difference between those two Pilots is the output iron - the SM245 has much bigger transformers. You'll see opinions and claims "out there" that the transformers in the 245 are the same as those used in the venerable SA232, but according to the SAMS folders for the two amps, they are different and they have different primary impedances. Still, they're about the same size and probably sound every bit as good.

Your 602 has smaller output transformers, but they're still Pilot transformers and they will sound very nice indeed. :yes:

 

[nerdorama]

Have you considered running any of these amps as triodes? I am seriously considering it for one of the HF81's. I'm wondering if I can get some of that SET magic I experienced with the 300B.

Hi Dmannnnn,
My experience with triode wiring of pentodes is that unless you reduce or eliminate the global feedback, you won't hear much difference other than a loss of gain. With the triode connection you can open the global negative feedback and then hear what happens. Now, there is never a free lunch, so with no GNF you won't have the same damping factor but it won't be too bad since the triodes will have a much lower plate resistance. You probably WILL have too much gain without the GNF though, and then you need to redesign the gain stages for optimal performance. It won't hurt to try it and see what you think. This very process was my first big experience with tubes. No going back after that.
Best,
John

 

[jaymanaa]

You could always get one of these and just be done with it. I don't know of anything running bigger iron in an EL84.

 

[Redboy]

You could always get one of these and just be done with it. I don't know of anything running bigger iron in an EL84.

Ummm...'cept it's a 7189 amp.

 

[Sam Cogley]

The OPT on my Fisher R-20 console chassis is enormous. Sounds great when the bloody thing is working.

 

[GordonW]

You could always get one of these and just be done with it. I don't know of anything running bigger iron in an EL84.

Um... maybe THIS?

'Course, that's not stock iron. It was made for a 6973 jukebox amp. And it's now a Stromberg circuit (this is the amp with the ASR333 amp circuit I was referring to in the first post in this thread)...

Regards,
Gordon.

 

[tube-a-lou]

Hiya,

What about the Scott 299-B or even the 299-A. I would put these up against most anything.

There are also the Fisher Variants but I have not restored mine yet so no comment.

Although I do regret letting my ASR-433 go but can't have everything right ???

Frannie

I agree with Frannie, I finally got a 299A (model 2) which I call it and
love it, it really sounds great with the Celestion 100 It has just the right
amount of highs, and it gets better and better when I change parts inside,
but I'm restoring it slowly, but so far I'm really happy with it.

Tube

 

[cubby01]

Um... maybe THIS?

'Course, that's not stock iron. It was made for a 6973 jukebox amp. And it's now a Stromberg circuit (this is the amp with the ASR333 amp circuit I was referring to in the first post in this thread)...

Regards,
Gordon.

Gordon, is that a volume pot under the OPT on the right? Since no tone control what's under the OPT on the left? I thought it looked like maybe a fuse but that didn't make since to me wiring-wise. Got a pic of the underside?

 

[jaymanaa]

Ummm...'cept it's a 7189 amp.

Depends how you bias it, and what tubes you are using.


What are the measurements of the OPTS Gordon, I'll take the cage off and measure these, you may be right.

 

[GordonW]

Gordon, is that a volume pot under the OPT on the right? Since no tone control what's under the OPT on the left? I thought it looked like maybe a fuse but that didn't make since to me wiring-wise. Got a pic of the underside?

Left control (nearest the end) is a source selector (3 input integrated amp). Middle control is volume. Right control is on/off.

Jay- I will have to ask the guy who has this now, to measure it. Though, they're about the size of Fisher 500 OPTs. Think Eico HF81 with about twice the lamination thickness of the Eico transformers.

Regards,
Gordon.

 

[jaymanaa]

Left control (nearest the end) is a source selector (3 input integrated amp). Middle control is volume. Right control is on/off.

Jay- I will have to ask the guy who has this now, to measure it. Though, they're about the size of Fisher 500 OPTs. Think Eico HF81 with about twice the lamination thickness of the Eico transformers.

Regards,
Gordon.

IOWs bigguns! Did the high frequency extension suffer from the larger TXs? Just curious as I've heard that is always a compromise issue. I put very small OPTs on my 2A3 amp because I planned to use it for 1k and up. Just curious as to what you experienced. Thanks Gordon

 

[Dmannnnn]

Hi Dmannnnn,
My experience with triode wiring of pentodes is that unless you reduce or eliminate the global feedback, you won't hear much difference other than a loss of gain. With the triode connection you can open the global negative feedback and then hear what happens. Now, there is never a free lunch, so with no GNF you won't have the same damping factor but it won't be too bad since the triodes will have a much lower plate resistance. You probably WILL have too much gain without the GNF though, and then you need to redesign the gain stages for optimal performance. It won't hurt to try it and see what you think. This very process was my first big experience with tubes. No going back after that.
Best,
John

Which amp was this? Have you done it with others?

I don't think the low damping factor would necessarily be a problem for me. I didn't mind it with the SET amps. Reducing or eliminating the feedback loop is what I expected. I'm not an anti-feedback fanatic but I would really like to put together an amp with a very simple and short signal path (using the HF81 as a starting point).