Options for 1974x Replacement Transformers

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junior marbles
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Options for 1974x Replacement Transformers

Post by junior marbles »

My Dagnall OT blew, but before it did, it sounded at least in the ballpark for that creamy (I hate that word) blowing overdrive, the kind that handled mid-frequencies and their complexities beautifully and came pretty close to the 'woman tone' (yes, I know those were KT66 and not EL84, but still...)

Anyway, I am underwhelmed by Heyboer's supposed copy of the RadioSpares dual-secondary OT as used in the original 1974: too bright, crystalline, and also way too much bass, lacking in midrange sex appeal that goes right to your gut- I tried to chance settings on the amp and my Les Paul, but did not come closer to a satisfying tone- nothing like even the Dagnall in terms of sweet distortion and approximation to a 1960s Marshall Combo.

What do I do now? I have the Dagnall rewound so at least the core, its laminations and annealing will be still the same. Any alternatives out there that tried to nail that sound and succeed?
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Re: Options for 1974x Replacement Transformers

Post by JMPGuitars »

You might want to break in the Heyboer. Those OTs sound pretty awesome normally. It sounds like yours needs to be used for a bit and broken in well. I'm guessing your old OT was well broken in.

Your other option would be looking at Mercury Magnetics. Which will also likely need some breaking in.
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junior marbles
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Re: Options for 1974x Replacement Transformers

Post by junior marbles »

Though the sound is pretty far off from what I expected, I will try "breaking in" the transformer, though I am unclear what exactly that means: there are no moving parts in an OT, and I cannot see what needs to be "formed", like with certain types of new capacitors....?
Anyway, how do you suggest I break in the OT? I can't play the amp 24/7...?
Thanks.
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Re: Options for 1974x Replacement Transformers

Post by colossal »

I am kind of surprised to hear you not liking the Heyboer OT. The Dagnall was never in the original 1974 circuit, of course, so I am interested to know how they wound that reissue OT and what primary it is wound to, etc. With the 1974x reissue, Marshall used a 91R bias resistor in the power section. The originals had 100-120R. The 91R coincides with Geoff's findings about the lower B+ with the reissues. The original RS OT has a complex interleaved winding and was made with M6 steel. I would like to know what Dagnall did for their version. My guess is that they did not do an interleave, and if they did, it is a simple one. Also, they probably did not use M6 to save cost. My other guess was that they wanted the amp to break up sooner, doing its "18W trick" earlier than a dimed amp would otherwise allow. But who knows, I am just internet speculating right now. I have found Mercury's RS to be very balanced sounding and the mids sound killer.
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Re: Options for 1974x Replacement Transformers

Post by JMPGuitars »

junior marbles wrote:
Mon 11/08/21 12:35 pm
Though the sound is pretty far off from what I expected, I will try "breaking in" the transformer, though I am unclear what exactly that means: there are no moving parts in an OT, and I cannot see what needs to be "formed", like with certain types of new capacitors....?
Anyway, how do you suggest I break in the OT? I can't play the amp 24/7...?
Thanks.
I dunno. It's a funny topic. Some people claim that new OTs might require at least 20 hours of break in. Others claim it's B.S.. My experience is that the Heyboers sound quite good, so I figure it's worth playing it more and see if it helps or not.

Thanks,
Josh
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Re: Options for 1974x Replacement Transformers

Post by junior marbles »

I have found Mercury's RS to be very balanced sounding and the mids sound killer.
Are you saying they offer their version of the interleaved RS used in the original 1974?
And are you also suggesting that, if I go with a Radio Spares copy, I should change out the bias resistor? Where can I read up on "Geoff's findings"?
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Re: Options for 1974x Replacement Transformers

Post by geoff 1965 »

If you check out GDS amplification you will see heyboer make 2 versions of the 18W output transformer,one is updated to suit modern amplifiers and the other is an exact replica of the original radiospares.
Marshall claim they built the 1974X to be close to the originals and we found that the PT has a lower HT of 275-0-275 @ 150mA loaded and is biased hotter,this corresponds with the “colin’s early schematic” in the downloads which shows a 300-0-300 HT “unloaded”
The radiospares el84 output transformers from that time were rated at 15 watts so that might be the difference you are hearing if Marshall specified the dagnall’s from one of those output transformers.
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Re: Options for 1974x Replacement Transformers

Post by colossal »

junior marbles wrote:
Mon 11/08/21 3:56 pm
I have found Mercury's RS to be very balanced sounding and the mids sound killer.
Are you saying they offer their version of the interleaved RS used in the original 1974?
And are you also suggesting that, if I go with a Radio Spares copy, I should change out the bias resistor? Where can I read up on "Geoff's findings"?
Yes, Mercury offers several versions, but there is one that is their take on the original. It's not absolutely spot-on to the original as far as actual construction methods are concerned, but it is the five layer interleave. They add a dedicated 8R lead where with the original, you'd have to select your impedance because of how the secondaries are wound (you can see this with the little tagboard that sits on top of the original's lamination stack).

No, I was not suggesting you change your bias if you decide to get a different OT. You should leave that where it is as the amp is designed with a different power transformer spec and operating point (see Geoff's reply on that).

Just today, oddly enough in fact, I had a conversation with a colleague who had just rewound a Dagnall for a 1974x and its construction is not close to the Radiospares. There are many changes, sadly (but unsurprisingly) mostly for cost reduction. Now, if you like the sound of the Dagnall OT, that's good enough for Rock and Roll.
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Re: Options for 1974x Replacement Transformers

Post by geoff 1965 »

That’s a good point from Colossal,and coincidentally the early dagnall PT’s were a failure point.if you search the “1974x PT replacement” post you can check if yours has the upgraded PT and there is the Marshall schematic in there.if you liked the dagnall why don’t you contact Marshall to see if they have replacements? they were very good in response to the guy who’s PT burned up.
This is a tricky one with so many variations mercury,heyboer,valvepower,Hammond etc which are all good and having no reference to the dagnall specs does’nt help.
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Re: Options for 1974x Replacement Transformers

Post by zaphod_phil »

geoff 1965 wrote:
Tue 11/09/21 4:53 am
That’s a good point from Colossal,and coincidentally the early dagnall PT’s were a failure point.if you search the “1974x PT replacement” post you can check if yours has the upgraded PT and there is the Marshall schematic in there.if you liked the dagnall why don’t you contact Marshall to see if they have replacements? they were very good in response to the guy who’s PT burned up.
This is a tricky one with so many variations mercury,heyboer,valvepower,Hammond etc which are all good and having no reference to the dagnall specs does’nt help.
The Hammond 125E has proven to be a great sounding OT for an 18W. Not quite in the same league as a Heyboer OT, but sounds fine all the same!
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Re: Options for 1974x Replacement Transformers

Post by zaphod_phil »

geoff 1965 wrote:
Tue 11/09/21 4:53 am
That’s a good point from Colossal,and coincidentally the early dagnall PT’s were a failure point.if you search the “1974x PT replacement” post you can check if yours has the upgraded PT and there is the Marshall schematic in there.if you liked the dagnall why don’t you contact Marshall to see if they have replacements? they were very good in response to the guy who’s PT burned up.
This is a tricky one with so many variations mercury,heyboer,valvepower,Hammond etc which are all good and having no reference to the dagnall specs does’nt help.
IMO< they should reference the original Radiospares' Transformer specs, not Dagnall, which AFAIK were primarily used by Marshall for cost-saving purposes.At the other end of the cost scale, Mercury appear to be crazy high-priced on account of the name :x
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Re: Options for 1974x Replacement Transformers

Post by geoff 1965 »

I agree, I was hoping the guy who posted the amp that was his uncles with the loose speaker wire would continue to post some pics & progress,that was obviously one of the early 18W’s but we did’nt get to see the transformers.
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Re: Options for 1974x Replacement Transformers

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geoff 1965 wrote:
Thu 03/24/22 12:32 pm
I agree, I was hoping the guy who posted the amp that was his uncles with the loose speaker wire would continue to post some pics & progress,that was obviously one of the early 18W’s but we did’nt get to see the transformers.
Hell yeah!!
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Re: Options for 1974x Replacement Transformers

Post by zaphod_phil »

junior marbles wrote:
Mon 11/08/21 2:19 am
My Dagnall OT blew, but before it did, it sounded at least in the ballpark for that creamy (I hate that word) blowing overdrive, the kind that handled mid-frequencies and their complexities beautifully and came pretty close to the 'woman tone' (yes, I know those were KT66 and not EL84, but still...)

Anyway, I am underwhelmed by Heyboer's supposed copy of the RadioSpares dual-secondary OT as used in the original 1974: too bright, crystalline, and also way too much bass, lacking in midrange sex appeal that goes right to your gut- I tried to chance settings on the amp and my Les Paul, but did not come closer to a satisfying tone- nothing like even the Dagnall in terms of sweet distortion and approximation to a 1960s Marshall Combo.
That might be because the original Radiospares OT was a budget Hi-Fi OT, complete with primary tappings for"ultraLinear" mode, primarily for use in the Mullard 5-10 DIY Hi-Fi amplifier
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Re: Options for 1974x Replacement Transformers

Post by sreiter »

From what I'm told by someone who has one of the largest vintage amp collections in the country, and was extremely close with Ken Fischer, Merren is the best transformer winder there is.

http://merrenaudio.com/
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