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Old 11th March 2011, 07:32 PM   #1
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Default Helios + Pultec tube EQ rack prototype.

I have just finished building a rack mounted all tube EQ prototype. One channel is a Pultec like passive EQ but with an added mid cut section. The other channel is a tube version of the classic Helios Type 69 passive EQ. here are a few pics:

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Cheers

Ian
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Old 11th March 2011, 11:19 PM   #2
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Very cool
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Old 12th March 2011, 10:04 AM   #3
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Ian, what's the reason for the bigger input transformer? Looks like a 1:10. If it isn't a preamp as well, won't it be fed from a line level signal? Or does it benefit in other ways?

Charlie
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Old 12th March 2011, 10:39 AM   #4
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Originally Posted by CSlee View Post
Ian, what's the reason for the bigger input transformer? Looks like a 1:10. If it isn't a preamp as well, won't it be fed from a line level signal? Or does it benefit in other ways?

Charlie
The bigger transformer is the output transformer - it is a 1:1 (600:600) type. The smaller transformer is the input transformer - it is a 1:1 (10K:10K) bridging type.

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Ian
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Old 12th March 2011, 10:41 AM   #5
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Ah OK, thanks
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Old 12th March 2011, 02:05 PM   #6
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Impressive build!
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Old 12th March 2011, 06:19 PM   #7
bichela is offline bichela  United States
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Quote:
Originally Posted by ruffrecords View Post
I have just finished building a rack mounted all tube EQ prototype. One channel is a Pultec like passive EQ but with an added mid cut section. The other channel is a tube version of the classic Helios Type 69 passive EQ. here are a few pics:

Click the image to open in full size.


Click the image to open in full size.


Click the image to open in full size.


Cheers

Ian
Do you have a schematic? I would be interested in looking at the design.
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Old 12th March 2011, 06:30 PM   #8
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Do you have a schematic? I would be interested in looking at the design.
Pultec EQP1A Equalizer - Pro Audio Equipment DIY - DIY Vintage Pultec (Pulse Technologies) EQP1A Program Equalizer
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Old 13th March 2011, 10:43 AM   #9
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Quote:
Originally Posted by bichela View Post
Do you have a schematic? I would be interested in looking at the design.
Here is the schematic of the Pultec part. It is somewhat modified from the original to allow the use of a 10K:10K bridging input transformer rather than the original 600:600 type plus mods to accommodate the additional mid cut.

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Cheers

Ian
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Old 27th August 2012, 06:04 AM   #10
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That is what exactly i was searching to include in the tube preamplifier which i will build as a companion of the SET monoblock power amplifiers.
Excellent work Ian! That is exactly what i like, a well documented and focused design. Very nice built! I will be in contact with you - if you allow me - for any technical advice in the near future.
Thank you in advance.

Fotis
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