5E5 transformer?

[stephenhartley]

Hi

After successfully building my first 5E3 based amp, I'm planning to build something similar but higher wattage - the Fender 5E5 pro seems to fit the bill (I'll change the tone circuit).

I'm looking for reasonably priced transformers and I've found an OT with the following spec (I'm in the UK) - can anyone tell me if it's suitable. Spec below:

Primary impedance:
Secondary:
Construction:
Dimensions:
Fixing Centres:
'drop-through' cutout:
Weight:
Incremental inductance:
Output Power:
Freq. response: 5.6 k Ω
4 – 8 – 18 Ω
high quality, 3-section, standard laminations
96 x 80 x 85mm
80 x 64mm
65 x 68mm
1.5 kg
> 100 Henries
25 – 30W r.m.s.
40 Hz – 12 kHz

[jmaf]

I don't see it mention a primary center-tap and since it mentioned incremental inductance I'd double check that this is not a single-ended OT.

[stephenhartley]

Thanks i I'll check it out

[MWJB]

Torresamps.com in Pinner & Ampmaker.com in Woodbridge have reasonably priced transformers that would suit.

BlueBell Audio in Dundee carry the Hammond range including the guitar amp drop in replacements.

Allparts UK carry some Mojo parts from time to time, cheaper than buying from TAD if you are in the UK (if they have what you want.

Don't rule out Doug Hoffman in the US either for parts, he turns round orders as quickly as most in the UK/Europe, probably less ideal for very heavy parts though.

The old tweeds tended to have a higher primary Z than current Fenders, you could try a multitap 3.5K:4/8ohms OT with both secondaries and see which you prefer? Blues Deluxe OT would also be ballpark with a matched spaker load.

Why change the tone circuit?

[stephenhartley]

5e5 transformer

Thanks very much for that. I'll research those options.

I'm working towards building a rugged amp that will do what the 2 amps that I've been using for the last 30 years will do (a beige AC30 & a Tolex tremolux) - namely a clean second channel that can be used for vocals (or even bass guitar) in rehearsals and even small venues.

I bought the tone mod from Bruce Collins for the 5E3 that I've just built and it's excellent but I'd like the option to dial in bass & treble in the way that I can on my Tremolux so I'm thinking of putting the Tremolux tone circuit into the 5E5 circuit (if that's possible? - I'm an electronics novice). The existing tone circuit (which seems identical to the 5E3) results in interference between channels (from what I've read)

[d. spree]

Thanks very much for that. I'll research those options.

I'm working towards building a rugged amp that will do what the 2 amps that I've been using for the last 30 years will do (a beige AC30 & a Tolex tremolux) - namely a clean second channel that can be used for vocals (or even bass guitar) in rehearsals and even small venues.

I bought the tone mod from Bruce Collins for the 5E3 that I've just built and it's excellent but I'd like the option to dial in bass & treble in the way that I can on my Tremolux so I'm thinking of putting the Tremolux tone circuit into the 5E5 circuit (if that's possible? - I'm an electronics novice). The existing tone circuit (which seems identical to the 5E3) results in interference between channels (from what I've read)

Stephen

What drove you to consider the tone mod and what did you find the effect to be? I am tweaking two 5E3s at present. Want to be able to play both my strats and my gretsch (with humbucking pickups).

[stephenhartley]

Hi

I'm working towards building amps that have two well separated channels mainly so that I can use one channel for vocals at rehearsals (which I've been doing for years using my Fender Tremolux).

I did a lot of reading of forums, all of which said that the stock 5E3 had early/low volume break up and lots of interaction between channels. I'm sure this is fine for just guitar.

I mainly use a Gretsch Tennessean and it sounds great. The Bruce Collins mod has plenty of top when turned up full (I use it about half way) and the channels are well separated. I've swapped the 5AY for a 5AX and the 5y3 for a 5V4 giving more headroom. With a delay the amp gives a great rockabilly sound and with my Vox distortion it has plenty of crunch and sustain. I also have it biased cool at 22mA.

I've never seen or heard an actual Tweed Deluxe (I'm in the UK) so I can't really give you comparisons.

Hope that helps

cheers

Stephen

[MWJB]

Are you running fixed bias or cathode bias, 22mA seems very low for cathode bias.

You wouldn't swap the 12AY for a 12AX for more headroom, especially if intending to use with a mic.

I'd try a 12DW7/ECC832 in V1, this will give lower gain & greater headroom on the mic channel and the instrtument channel will sound as it does now.

What mic are you using, are you using an in-line impedance transformer?

[stephenhartley]

Cathode bias using a 500R resistor - someone suggested that that was far too high and that I might have a dry joint or a faulty cathode bypass cap. I replaced the cap and went through the entire board. I did find a couple of faulty contacts and replaced them. I also tried replacing the 500R with stock 250R and the amp broke up at a lot lower volume and just didn't sound as good. I'll certainly try a 12DW7/ECC82.

I also had a lot of hum on the mic channel. I've managed to reduce it (but not get rid) by soldering the 68k V1 grid bias resistors directly to the valve base and running screened cable to the sockets.

I use standard SM58 type vocal mic plugged straight in.

[MWJB]

"I also tried replacing the 500R with stock 250R and the amp broke up at a lot lower volume and just didn't sound as good" - There is no "stock" value, there is only the value that correlates to your power tube plate voltage & tone desired (without burning anything up, of course). In this design the 6V6s often like to see 30mA at least, so maybe try a 330ohm, or 390ohm resistor.

Try a Shure A 95-UF impedance matching transformer between the XLR-XLR cable & the amp's 68K #2 input. The hum is probably related to grounding, the 68Ks should be & are fine normally when mounted on the input jacks. IIRC Bruce's mod uses a ganged 2x1MegA tone pot, for the mic channel it might be an idea to fine tune any bright caps on the mic volume &/or tweak the mic channel tone pot value by bridging the 2 outside pot tabs wih a smaller value resistor, like perhaps 220K?

[stephenhartley]

Thanks very much for that - I'll experiment.

My next build is another 5E3 based circuit but in a smaller 1 x 12 cab. I'm going to separate out the tone pots. I've been looking at the tone circuit on the Marshall 2061 lead/bass 20 and I thought I might experiment with that.

After that, I'm going to try a 5E5 - I've gathered all the parts.

I'm puzzled by the input on the 5E5 schematic. There are no grid stopper resistors. I'm thinking that this must be related to the use of a separate pre-amp tube (the circuit otherwise looks very similar to the 5E3)

I'm avidly trying to learn about the electonics as I go along and I've picked up several books. I've been reading Merlin Blencowe's 'Designing Tube Preamps for guitar and Bass' and he says that the grid stopper resistor can be much lower than the 68k routinely used on many vintage amps - he recommends 33K or even as low as 10k. What difference would that make to the sound?

[Bruce / Mission Amps]

Those 68K resistors are NOT used as a grid stoppers. The two 68K resistors are used as a voltage divider so you can either loose a little input signal in the low jack or use two instruments (or a mic and one instrument) into one single channel.
There are no grid stopper resistors on the preamp stage.

Look very carefully at a black face Princeton schematic.
That amp is very similar to what you are describing as your new desired circuit.
The major differences being the vibrato circuit, which you might not want, the BF treble, bass, (+ mid setting resistor) tone controls, how the volume pot is wired and the fact that the BF Princeton is using a fixed bias supply for the power tubes and you want cathode biased power tubes if trying to keep some of the tweed mojo.
In this instance I would say use higher B+ voltages then the 5E3 but use 390 ohms to 470 ohms for the cathode biasing of the power tubes and it will sound very good.

[stephenhartley]

I'm presuming that that's the AA964 - I have Gerald Weber's book, and I've looked at the schematics in there. I don't want the vibrato. There's only one channel in the Princeton though and I want 2. The 5E5 circuit seems to be ideal. I need to keep it simple. I'm still a novice.

I'm struggling to get rid of the hum on the mic channel of my 5E3 build - the instrument channel is fine though. I suspect a lot of is because of my chassis layout (I've built it 'upside down' like the tolex Fenders, but I didn't think to swap the components accordingly - consequently the input sockets are at the opposite end of the chassis to V1. I have another thread on the go on here, and have been getting some helpful suggestions. Would changing any of the cap or resistor values on your tone circuit make any difference?

Because the amp is upside down, the tone circuit has ended up back to front.

[Bruce / Mission Amps]

Use the other triode for the other channel but use one plate load resistor! A common 47K to 56K plate load resistor and two separate cathode biasing resistors.
The 47K to 56K common plate load resistor should mix the two triodes to one common tone stack and volume pot.

[stephenhartley]

Looking at the 5E3 schematic, does this mean that I replace the 2 100K resistors from pins 1 & 6 of V1 with a single 47K to 56K and remove the jumper from pins 3 and 8 and add a separate 820R resistor from pin 3 to earth with a 25/25 cap in parallel?