DCAudioDIY.com

DC Area Audio DIYer's Community
It is currently November 5th, 2024, 2:07 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 26 posts ]  Go to page 1, 2, 3  Next
Author Message
PostPosted: September 19th, 2024, 9:59 am 
Offline
User avatar

Joined: December 14th, 2013, 2:19 pm
Posts: 985
I'm going to build an amp for my son. I have two complete sets of transformers, output and power. One from an HH Scott 290 and one from an Eico HF87. Any idea which might provide higher quality audio? The amps are both rated for ~50 watts or so. Both used EL34 output tubes. I'm gonna be building Oddwatt type amps again, so I can use EL34, 6L6, KT66/77 types or 6550/KT88/90/120/150.

I couldn't find specs for the transformers. In my present Oddwatts, I'm using Stereo 70 outputs, but with 8 ohm loads on the 4 ohm taps. Amazingly, even with 180mA standing current (Class A), the outputs stay cool to the touch. My point being that current won't be an issue, and I'll select different taps as needed for best performance.

The Scott is often compared to Marantz amps of the day (early 60's). The HF87 is also well known for decent performance.

Thanks for any input about the outputs.

Stuart

Attachment:
290.PNG
290.PNG [ 394.34 KiB | Viewed 4050 times ]


Attachment:
scott_290_stereo_power_amplifier_sch.pdf_1.png
scott_290_stereo_power_amplifier_sch.pdf_1.png [ 89.54 KiB | Viewed 4050 times ]


Attachment:
HF87.PNG
HF87.PNG [ 436.27 KiB | Viewed 4050 times ]


Top
 Profile  
 
PostPosted: September 19th, 2024, 10:03 am 
Offline
User avatar

Joined: December 14th, 2013, 2:19 pm
Posts: 985
HF87 schematic. I couldn't post it in the previous post for some reason.


Attachments:
Schematic.PNG
Schematic.PNG [ 94.78 KiB | Viewed 4049 times ]
Top
 Profile  
 
PostPosted: September 19th, 2024, 10:23 am 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1749
Location: Parkville, Maryland
This old Geezer understands that EICO and Heathkit designed kits around major brands. They were both known for their output transformers in terms of audio quality. :character-oldtimer:

Since both the H.H. Scott and the EICO amps were designed for 6CA7 (EL-34) tubes I doubt you could go wrong with either choice.

Flip a coin.

_________________
Walt


Top
 Profile  
 
PostPosted: September 19th, 2024, 5:54 pm 
Offline

Joined: April 22nd, 2013, 12:58 pm
Posts: 293
The Eico uses a voltage doubler for the B+ supply, which is not the best.
170V @ 0.9A
6.3V @ 7.6A
75V for bias
The Scott 290 has a beefy full-wave design.

Image
https://audiocircuit.dk/downloads/hhscott/HHScott-290-pwr-sch.pdf

As for the outputs, the Eico has Ultralinear taps similar to your Dynaco. The Scott is straight Pentode operation.
The exact OPT aren't listed here, but it's a good cross section of OPTs (for your next restomod... LOL)

https://www.one-electron.com/Projects/trans_p1.pdf


Top
 Profile  
 
PostPosted: September 19th, 2024, 10:05 pm 
Offline

Joined: June 4th, 2013, 2:39 pm
Posts: 497
What Bruce said. The HF-87 was only 35 wpc, but UL. The Scott will probably give you more power but in pentode mode. The Eicos are probably a bit "sweeter". Also, the Eico power tranny is surprisingly small and runs pretty hot. Both are nice output transformers, I don't think there's any need to quibble about that. ;-)


Top
 Profile  
 
PostPosted: September 19th, 2024, 11:23 pm 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1705
Just build them both, and let us know ;)

Roscoe

_________________
I can explain it to you, but I can’t understand it for you.


Top
 Profile  
 
PostPosted: September 20th, 2024, 1:16 pm 
Offline
User avatar

Joined: December 14th, 2013, 2:19 pm
Posts: 985
Thanks to you all.

Based on conversations with David M., I'll build the Eico/Mullard circuit for my son. The only significant changes being a CCS in the phase inverter tail with equal value plate loads; powering the 12AX7 and 6SN7s from a dedicated DC power supply; ultrafast diodes; and upgraded cap values and types (DC Link in the power supply for instance).

Yes, Grover, I'll leave plenty of room around the power transformer, and take the heater loads off of it, onto a second transformer.

Now, to lay out a PC board!

Stuart


Top
 Profile  
 
PostPosted: September 20th, 2024, 1:52 pm 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1749
Location: Parkville, Maryland
Stuart Polansky wrote:
Now, to lay out a PC board!Stuart

Party on! :obscene-drinkingcheers:

_________________
Walt


Top
 Profile  
 
PostPosted: September 20th, 2024, 3:29 pm 
Offline

Joined: April 22nd, 2013, 12:58 pm
Posts: 293
The DynaMutt PC boards used to be a good option for that circuit. I'm not sure if they are still available.

https://music-electronics-forum.com/attachment.php?attachmentid=27479&d=1392301326


Top
 Profile  
 
PostPosted: September 20th, 2024, 4:27 pm 
Offline

Joined: June 4th, 2013, 2:39 pm
Posts: 497
Don't forget the 750pF cap across the "upper" OPT primary. I assume it's there to equalize the winding capacitances (or something like that).


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 26 posts ]  Go to page 1, 2, 3  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group