Replacement output transformers for Fender Blues Junior 3 amp?

[Mark]

I was wondering if anyone had upgraded the output transformer in a Blues Junior mark 3?

I have a friend who wants more bass and mids from his amp.

I have noticed that Mojotone use to sell one, Allen’s amps use to sell them only domestically, Mercury sell them but I have not idea what is different from the original transformers?
Then there is Soursound’s transformer which my friend baulked at because of the price.

https://www.mercurymagnetics.com/produc ... ransformer

http://allenamps.com/trans.html

https://fromelelectronics.com/collectio ... s/blues-jr

https://fromelelectronics.com/collectio ... ransformer

[martin manning]

For more options, a 2x 6V6 i.e. Deluxe Reverb OT or upgrade would be fine for this.

[Stevem]

More bass and mid’s when?

While playing clean , dirty or both?

A more efficient speaker ( db rating wise) and putting sound absorbing material in the cab to line the two side walls the bottom and the lower rear panel is where I would start.

I would also circuit wise parallel a 100uf 500 volt filter across the first filter node cap that’s in the amp now.

Groovetubes output tubes in a number 10 will help out like 5% with more head room before the bottom end response gets flabby.

Also the speaker that’s in there if original might just need to be broken in .

Once this is done the amp will have far more bottom and mid’s with the amps volume at a lower setting then normally used at.

Playing the amp takes far to long a accomplish this break in so I would use the low voltage ac wall wart method.

[pdf64]

I was wondering if anyone had upgraded the output transformer in a Blues Junior mark 3?

I have a friend who wants more bass and mids from his amp.
...

How has the design of the stock OT been identified as the cause of the combo's insufficient bass / mid output?
eg they've tried a different amp through the BJ cab and that's resolved the weak tonal balance?

[Smitty]

Mark Abbott has been posting here since 2005 and is a prominent contributor in the Trainwreck forum.

https://ampgarage.com/forum/viewtopic.php?f=1&t=23

Transformer upgrades for Blues Juniors are well recognized and fairly popular because of the size of the originals.

Mark,

Martin's advice seems solid. Although not in Blues Jrs, I've had good success using vintage Hammond organ AO-43 output transformers. Looks like Mark over at Frugal Amps might be selling one on ebay:

https://www.ebay.com/itm/135615803041

[solderhead]

I have wholesale accounts with two of the boutique transformer suppliers that the OP has mentioned. I've purchased LOTS of transformers in bulk over the years, often 25-50 units at a time.

If it were my amp, running to change the transformer would be at the bottom of my to-do list. There are just so many other options that are likely to yield positive results that I wouldn't start off with an expensive transformer swap that's based on faith that there's some sort of magic fairy dust embedded within one company's product. IMO there's been far too much BS marketing by a popular transformer manufacturer (you know who), with the intent to con everyone into believing that every amp needs to be upgraded with their premium priced product to transform every amp into something with capabilities beyond what the original manufacturer was capable of producing.

First and foremost, a speaker change is going to provide a huge difference to the amp's tone, and will probably be most effective in changing the sound of an amp. Frequency response can be tailored using physical means to adjust the response of the cabinet like those mentioned by SteveM. Looking at the robustness of the PSU and the f3 points for the high pass filters present in the amp would also be a good place to start. Changes there cost almost nothing. I have used DR OT for EL84 applications as Martin has suggested, and they do work very well with EL84 and they have a very good full range sound -- though the cost of buying a DR OT would make it the last choice on my list.

Here's something interesting that I found online when I looked up the definition of "mercurial" at Miriam Webster:
https://www.merriam-webster.com/dictionary/mercurial

2
: having qualities of eloquence, ingenuity, or thievishness attributed to the god Mercury or to the influence of the planet Mercury

My advice would be to exhaust all of the simple / inexpensive circuit analysis options before committing to an OT upgrade.

[Smitty]

Funny. I've always thought is was ingenious how Mercury were able to make their transformers sound thievishly eloquent.

[Mark]

Thanks for the replies.

The output transformer is minuscule in this amp, it’s easily smaller than a Champ output transformer by a reasonable margin. Bill M first proposed changing out the output transformer.

The 0.0022uF caps C1 and C16 long gone via a previous Fromel/Bill M mod. In short it has had the typical mods done to it and it still lacks mids and bass regardless of whether it is clean or distorted.

I have heard from another friend that he likes Greenbacks in them while another friend swears by 65 watt Celestions. I don’t want to propose a particular speaker to my friend as one man’s meat……

Again thanks for your assistance.

[pdf64]

The output transformer is minuscule in this amp, it’s easily smaller than a Champ output transformer by a reasonable margin.

Champs are single ended, all else being equal, single rnded OTs need to be much bigger than push pull.

I have heard from another friend that he likes Greenbacks in them while another friend swears by 65 watt Celestions. I don’t want to propose a particular speaker to my friend as one man’s meat……

Might the takeaway from the above be that a decent speaker will probably improve the sound?
Did your friends that like Celestion speakers in there also change the stock OT to something bigger?

[martin manning]

I have no direct experience with Blues Jr's, but speaker auditions are always interesting. In this case people seem to prefer Celestions, but of course in the end it's personal preference. Re the output transformer, several suppliers have offered upgrades, so I would tend to believe there is something to be had there. In both cases it's probably a safe bet that the OEM parts are a compromise to hit the price point. Unfortunately, both of these items are expensive, and most people don't have samples lying around to try.

[solderhead]

Want to find out how much bass you can get out of a good speaker swap? Hook up the electronics to drive a 4x12 or a single EVM-12L in a TL-806 Thiele ported cabinet. If you can't get good bass with either of those setups then further speaker experiments won't help much and it's time to move on to transformers. But be forewarned, that's an expensive / low-yield proposition and it's not as much fun as auditioning speakers.
--
A "proper" single-ended OT uses an air-gapped design. That makes it much larger in size than it's push-pull counterpart. According to proper HiFi design standards, an SE OT should always be air-gapped, with the result that if you follow the rules, it will typically be larger than it's push-pull counterpart. That really makes it difficult to look at a properly designed SE OT and compare it with a properly designed PP OT. It should be larger, but my how much? Their designs are very different and that makes direct comparisons difficult.

What complicates things is that the type of SE OT that we get in guitar amps are almost never properly designed (by HiFi standards). As a general rule they're never air-gapped and that does make them much smaller. When cost-conscious producers manufacture SE OT they tend to avoid air-gapping the designs and use compact winds. This simpler winding method greatly reduces production cost.

Fender was the master of cheapening parts designs down to their bare minimum to lower production cost. Through serendipity, and breaking the rules for "proper" design Leo came up with some absolutely fabulous results. It's not clear whether this was intentional or just dumb luck.

Back in the Tweed Era they made Champ OT that were so small that it was evident they were breaking all of the rules to make transformers as cheaply as possible. This ended up having some positive but unintended consequences, like the 59 Tweed Champ who's OT was smaller than a golf ball, but produced incredible tone when the amp was driven wide open to saturation (think Clapton/Layla sessions).

Back in the 90s I took a deep dive into this area, and I bought boutique repros of every variant of the Tweed/BF/SF Champ OT that were ever produced. I think there were 12 to 15 of them in total. I built a modular chassis that allowed actively switching between each OT in the series for tonal comparisons. It was amazing to learn that some of the "worst" designs ended up having some of the best tone in certain applications, but sounded absolutely horrible in other applications. Sometimes breaking the rules works. Sometimes it doesn't. Clapton was one of the first people to learn that the old Tweed Champ sounded so good when it was run wide open, even though it didn't sound all that great when used as it's designers had intended.

I'd like to post a photo of that Champ switching chassis in this thread, but I regret that I can't find it. I thought I had kept a photo but I just looked for it and I couldn't find it. I've changed computers several times since the 90s and likely it's on an old hard disk that's in a box somewhere... or on a disk that crashed long ago. Unfortunately the photo is long gone.

This post is sort of a long, roundabout way of saying that you can't always predict a transformer's performance by looking at it, and the same OT that may be disappointing for one particular application may be absolutely outstanding in another application. The problem that you run into is that iron-rolling is a very expensive proposition for the end-user. It wasn't a big deal for me because I was buying and selling lots of iron while I was doing design research. I paid my money and took my chances and learned along the way.

So what's my point? The Blues Junior is a great amp -- many people love it exactly as it is. Some people don't. Some people (especially those in the HiFi world) will tell you that the small-bottle EL84 have no chance of ever producing respectable bass and that you need to move to big bottles to get that. For those people who aren't satisfied with a BJ or 2xEL84 then a different amp makes the most sense. My advice would be to avoid the temptation to start rolling expensive transformers into an inexpensive amp to try to change it's bass response. If simple mods to the voicing of the circuit don't work, and a speaker change doesn't work, then get rid of the amp and buy something that sounds good as it is. It's almost guaranteed that it'll be cheaper to buy a used amp that already sounds good than to throw money at trying to fix something that doesn't sound good. The world is full of inexpensive used amps, and sometimes the best bargains are to be had by trading-off an amp that you don't like. I know, I know ... there's a badge of honor that you get to wear when you mod an amp that sounds bad to make it sound good ... and we all like earning those badges ... but sometimes those badges end up costing more than just getting out an amp that's not working for you.

[Stratscratcher]

I have a Blues Jr. that I did almost all the BillM tweaks to it and I also replace the output transformer and speaker. The amp now sounds pretty good, before it had a crappy bottom end and I feel that the Allenamp output transformer helped a bit. I did another Blues JR. for a friend with the BillM tweaks and used a Mercury Magnetics output trans and it sounds pretty good also. The Allenamp transformer was not available when I did the second Blues Jr.. The BillM tweaks: Tone stack, coupling caps, Bias, Reverb (and reverb tank), power caps were all done, along with the output transformer and Lil Texas neo speaker, changed the knobs to red ones(that did the trick)...Transformers are expense and I think it helped a bit but, I also think If I hadn't tweaked the circuitry I would not be happy with the amp.

[solderhead]

Which transformer from MM? Did you use their BJ enhanced-mojo APS OT (link below) or did you upgrade to a DR-type OT as Martin had recommended? Or did you buy something in between?

My understanding from having a lot of transformers pass through my hands, including conversations with the people who actually wind them, is that all of the smaller Fender OTs are non-interleaved, including the Deluxe Reverb. The winding methods are all very simple, where they just wind the primary, then the secondary, without interleaving them. Someone please correct me if I'm wrong on that.

AFAIK all of the 2-hole mounted Fender OTs for the small amps are wound the same way (cheaply, secondary over primary). Barring any specific lamination upgrades (which the seller is certainly going to pitch to you in their marketing) or changes in wire gauge, then the OT size is the major variable to assess when shopping. I honestly doubt that one boutique OT is going to outperform a generic OT if they both have the same primary, they're both wound the same way and they both use the same amount of the same materials. The actual transformers won't differ much, but the price differences can be huge.

A replacement DR OT can be had from AES or Mojo for about $50. MM's over-sized offerings for the enhanced BJ OT come in at $163-$208. https://www.mercurymagnetics.com/model/blues-jr/

Looking at the MM BJ page, I see some 8k transformers that are probably wound the same way that everyone else winds them (ie: they advertise them as being clones of the originals), but they are oversized with respect to a BJ OT and will need chassis modification/hole drilling to fit.

In that context, it does not appear that MM is actually building a 'better design' OT for the BJ; it seems more like their marketing is telling you that the mojo comes from adapting a larger OT with the same primary specs, that was likely originally designed for a different amp but is being marketed as a BJ upgrade. I view that as an endorsement of Martin's suggestion to just buy the DR OT.

So we're looking at 4x the retail price to obtain the boutique OT compared to a generic DR OT. At wholesale the cost for a boutique OT would still be 2x the retail price of the DR OT. Only you can decide which choice provides more value to you. That said, I could sell someone an expensive transformer that is marketed to have built-in mojo, but I would only do so after telling them that they might not be any better off than if they just bought the DR OT.

The boutique manufacturer's product is significantly overpriced. Back in the day I used to be able to buy iron from MM that was cheaper than it's Hammond equivalent. Ever since they began mojo-marketing their prices have risen dramatically, so that Hammond is now much cheaper. When looking at transformers that are equivalent I choose the cheaper supplier. I don't buy from the boutique supplier unless I absolutely need a complex part that can't be sourced elsewhere and I'm willing to pay through the nose to get it.