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Some of you may know, we have been using and promoting the excellent s2 transformers with our kits and built into all of our amps. We are currently testing two custom output transformers built specifically for us by Heyboer Transformers*. One was a Radio Spares Clone and the other was the 'standard 18 Watt construction, with changes. We received the two models a week ago.
We recently started to comparison test the three brand new OTs. All three were mounted on a board and sequentially plugged into the output circuit of an sIII. Our first impressions are very encouraging.
Right off the bat, the Radio Spares Clone has a broader frequency response, especially in the high end. The clone exhibited clean high ends with no extra ‘fur’ on the high notes. This provided a full, rich complex and smooth tone. First impressions were that with the full but not overly hyped bass and clearer highs than all samples. It was smoother and slightly more compressed.
The other transformer was similar in construction to several 18 watt transformers you can purchase from various dealers. Again, as with the clone, this sample exhibited clean high ends with no extra ‘fur’ on the high notes. There seemed to be slightly less bass response than the s2. First impressions were equal to the s2 standard we have been using but with a clean high end and marginally less bass. The clean high end is inherent to the transformer.
We expect it will take some time to ‘burn in’ all of them as all 3 test samples are brand new. That may result in some smoothing of tone – we’ll have to see. Another week perhaps less.
Lawrence and I plan to do a QA test on all 3, and provide comparison sound clips for people to 'vote' for their favorite – and getting feedback on it. That will be interesting. We'll do that on our forum soon.
Radio Spares Clone
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This output transformer is wound the same as the original Radio Spares transformer used in the early Marshall 18 watt amplifiers. Because the M-6 grade today is a better quality than early 60's M-6, we decided to use M-27, or lower grade lamination material. This was done to capture the tone of the original 18 watt amplifier.
The clone has more interleaves /splits than other 18 watt transformers and this is probably what gives it the extended frequency response. The original RS deluxe was closer to the hi fi end for an output transformer. The clone is very close to the original 18 watt in construction electrically, mechanically and has a stand-up channel mount.
Our objective was primarily to get a Radio Spares Deluxe Clone that was versatile, vintage sounding and able to be use it in many amps with variations. So in addition, to the 8K primary designed for two EL84/6BQ5, we took the Ultra linear taps from the original design and changed the ratio ever-so-slightly to provide 5K taps for a 6V6 concept 18 watt amp. With this, conversion of an sIII to a 6V6 model would be simplified. In fact, the transformer could be used strictly for a 6V6 based vintage amp! The primary impedance for the clone is : 4k - 2.5K - 0 - 2.5K - 4K from center or 8K center tap on the outside and 5K center tap on inside leads.
Specifications
Construction
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All transformers tested were stand-up channel mount, direct replacement
EDIT *** The outside diameter of the windings on the Heyboers were about 1/8" larger than the s2. ***
RS Clone output transformer
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18 Watts
EL84 OR 6V6 push-pull
Interleaved windings
8K Ohm primary impedance
5K Ohm primary impedance
4 Ohm secondary
8 Ohm secondary - separate from other 8 ohm secondary
8 Ohm secondary tie two 8 ohms in series to achieve 16 Ohm secondary
M-27 grade steel laminations
3.5" mounting centers
Stand-up form
Flying leads
18 watt RS Color Coding:
Primaries: Blue - blue = 8K , White - White = 5K, Red = Center tap
Secondaries:
Black - Green = 8 ohm
White = 0
Red = 4 ohm
Blue = 8 ohm
Note: The clone has two separate secondary windings. To get a 16 ohm impedance, connect two 8 ohms taps are connected in series i.e. tie green to white for 16 ohms across black to blue.
Other output transformer
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This output transformer is similar to our standard s2 model, and to other 18 watt transformers available. It is an 18 watt capacity with 8K primary impedance 4-8-16 ohm in a stand-up channel mount.
18 Watts
EL84 push-pull
8K Ohm primary impedance
4 Ohm secondary
8 Ohm secondary
16 Ohm secondary
M-27 grade steel laminations
3.5" mounting centers
Stand-up form
Flying leads
18 watt Color Coding:
Primary
Brown - Start
Red - Center tap
Blue - Finish
Secondary
Black = 0 ohms
Yellow = 4 ohms
Green = 8 ohms
Orange = 16 ohms
Power Transformer
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To round out the set, we chsoe the PT -290. It features 120/240 volt primary for 60hz. Secondary is 290-0-290 HV, 6.3 V center tap heaters, 5/6.3v rectifier taps
Price for the sets are still to be determined.
*Heyboer Transformers has been designing and building the highest quality transformers for the electronics industry since 1958, serving customers worldwide. They have two West Michigan manufacturing locations.
_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps
Last edited by coco on Sun Apr 30, 2006 9:39 am, edited 4 times in total.
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