What makes an amp the best Harp Amp?

[Bruce / Mission Amps]

Without going crazy with a wish list.... what features makes your dream harp amp the best usable, all around harp amp you can think off?

Overall size, weight, ... type of power tubes, ... cathode biased, ...fixed bias, ...what phase inverter type, ... final output power, ...the actual type of coupling caps, ... number of speakers, 8"s, 10"s, single 12", 12"+8", single 15" ... a line out, ... single tone control or separate bass and treble tone controls, ... how about the worst case actual cost?
Give me some feedback here, I'm itchin' to use up some old tweed chassis of mine and build a few harp amps.

[overdrive]

I don't play harmonica but an acquaintance who does ran these two web pages by me...

www.harpamps.com/ampg/ampg10.html

Keith's Amp Picks

For those of you that are still confused or need to be hit over the head, here are my suggestions on what amps to consider.

Small Amps
Every Bluesman needs a small practice type amp that is light weight and still sounds good.

My choices.

Any amp with a 5Y3, 6V6, and a 12AX7 tubes with an 8 or 10-inch speaker.

Examples:

Fender Champ - Tweed is best because it sounds raunchy, but all before about 1970 sound good.

Gibson Skylark - The white tolex kind from the 50's are my favorite, the later ones are not as loud or nasty sounding. I got mine for $75 and will never sell it.

Premier 50 with the 12AX7 tube about 1960 - This is my favorite amp.

Small Valco amps from the late 50's and early 60's - This includes Harmony, Silvertone, Supro, Danelectro and National amps. I have a Valco National that has the exact same circuitry as a tweed champ.

Medium Power Amps
These are Fender Tweed Deluxe style amps from the late 50's and early 60's. They have usually two 6V6 tubes and a 5Y3 rectifier. They have 2 or three 12AX7 tubes and a good one will have reverb. These can cut through the guitar players at a jam, but may have to be miced. They have a 12-inch speaker or 2 10's.

The best choices are:

Fender Tweed Deluxe - This is way out of my price range.

Fender Princeton - Not the Princeton reverb, but the smaller amps based on two 6V6 tubes. The silverface amps are even good for harp. These are too tame for many guitar players and can still be had for under $500. The silverface might go for under $300.

Premier Model 120. The ones from the early 60's are the ones I like best.

Gibson GA-40 from the mid 1950's - This is a killer amp.

Big Amps
If you have to cut it with guitar players, your best bet is to get something with 2 12-inch speakers or 4 10-inch speakers and 2 6L6 tubes.

1959 Fender Bassman. This is the holy grail of harp players. It had a 4x10 speaker configuration and minimalist circuitry. I found the one I played through to be too sensitive and got a lot of feedback, but everyone swears by them. This amp is the basis of most boutique harp amps.

Sears Silvertone 1483. I have been told this is the best alternative to a '59 Bassman that you can get and the heads go for about $75. The cabinets are very cool and you can slide the head into the back of the cabinet for transportation. For $150 you can get an amp combo that sounds even better than the bassman.

Premier Model 71. This is a buttery smooth amp that breaks up nicely and resists feedback. This is my favorite big amp.

Older Ampeg Jets and ReverberRockets. These are great harp amps and readily available at affordable prices.

Gibson GA90 - I am told this is one of Kim Wilson's favorites. It has 6 8-inch speakers. They are way too expensive for my wallet.


There's also an interesting ongoing 6L6 harp amp build project at:

Lone Wolf Harp Amps

Lone Wolf Blues Co.

[MWJB]

Pretty open ended Q there Bruce...

Let's assume we are talking about a regular stage amp to be used with typical 40-50W guitar, bass & drums:

4x10 Fenders are hard to beat, fixed bias punch, 4 light 10" speaker cones help keep front to the note, a good bassman or Brown Concert...a lot of guys like Super Reverbs, I do too but prefer a 12AX7 in the PI & find the 6G#A style presence very useful. A bit of voltage dropping on the SR preamp wouldn't go amiss either (I like 160-180vdc on tolex preamps running 12AX7). I'd recommend 480-525vdc on the 6L6 plates, if the PT will take it EH KT90 will give better dynamics & headroom (bias to 8-15mA per tube). It's no accident that tweed bassmans & Brown concerts are the most popular harp amps. Concert is harder, more aggressive due to tighter cab, but great for blues chromatic.

Multiples of 10" are my preference, possibly mixed with 8" (wouldn't recommend just 8" unless for studio use). I have tried & tried & tried to make 12" competitive but always found increased feedback curbed available output in A/B comparisons. Even converted my SF twin to 2x10"...would consider a 4X10" cab for it too.

For smaller amps 2-3x10"...if looking to exploit high plate current designs I'd stick to 2x10", speakers arranged vertically (to minimise feedback), also 2x10" if looking for a good compromise between harp & guitar (high current with 3 & 4x10" = feedback hell). Brown tolex Bandmaster is killer out of the box (but serviced), gives away a lttle headroom to the 4x10"s.

If using 6L6 for gigging then I'd go with treble/bass/middle (usually need to roll off some bass for good cut/fidelity), for 6V6 a single hi cut tone pot is usually fine (& for 6L6 in recording/lo volume situ's).

Some guys love 15" for their tone (Harman, Wilson, Buffalo Norton), but be prapared for it to cut around a third off percieved volume compared to 4x10"

For gigging - always fixed bias, unless using a cathode/fixed switch. Love cathode for recording/low volume...even have a couple of self split amps for that purpose & quiet gigs. In many cases I found that 6L6 & 6V6 in cathode bias sound best without a bypass cap (less stiff, less feedback). 3 & 4x10" can be biased cool (<20mA) with Sovtek 5881, or Phillips 6L6WGB to curb feedback. 2x10" bias to regular currents.

Contrary to common consensus, I ALWAYS prefer a SS rectifier in medium & large amps, only use a tube recto in my champ. 95% of the amps I know are gigged with SS rectifiers.

Kim Wilson's most used gigging amps are Super Reverb, Brown Super & Brown Pro. I think that the GA 90 may have been used at a session (never confirmed) but a feedback monster to gig with. He has also claimed to use a champ for recording...he owns plenty of amps, so you can never be sure.

[Bruce / Mission Amps]

Yeah, it was a little opened ended but when I ask the locals around here, (and there are a few good ones) I get two or three different answers from each of them!!
In other words, there doesn't seem to be a solid general consensus about what makes a great harp amp except it has to be loud enough to be heard over the guitar player or drummer and needs to be feedback resistant.
I have about 20 chassis and 1X12 tweed cabs I must to use up as over stock inventory and have been wanting to do another harp amp but... man!!!
Some of these suckers are about as hard to work with as wanker guitar players! ha ha

My plan so far is; 25 watts, two 6L6s and two preamp tubes.... a mix between a Masco 18, tweed 5F4/5E5 and a GA 6 Gibson and with a variable line out.

Any others?

[arnenym]

I believe youre on the right track Bruce. 5E5 is a nice circuit.
Mixed speaker sizes give the best of two worlds. If you not have enough room for 1x12 speaker in combination with 1x10 you can try 1x10 and 1x8.
i dont think i can recommend one size of speaker cause one amp works fantastic with a 12 and another is better with 2x8 or 2x10. It depends on how efficient the speaker is and how much you have to turn the amp up before it begin to breakup in the preamp.

[MWJB]

Perhaps consider converting a 1x12" baffle to a single 10" and use a cleaner speaker like a Fane AX/AXA if 10" & 8" won't fit together? I have found the Emi Alpha 12" to be reasonably feedback resistant...but that was at cooler plate currents, 15-20mA (if you just really, really had to go with a 12"), the stock Blues Deluxe ceramic 12" Emi isn't too bad either.

If the amp is for gigging I'd seriously consider a global NFB loop. For a pair of 6L6 in a mid-sized gig amp (drums & restrained guitar & bass), I'd really be looking for 440-470v on the plates.

[pdf64]

My experience of a fane axa12 is that they have significant power compression, more so than a celestion gold. Even though they have high sensitivity at low power levels, they start to lose efficiency at about 20 watts and plateau out at about 30 watts, ie higher power input doesn't result in higher sound level.

[Bruce / Mission Amps]

Thanks for all the feedback, I really appreciate any and all comments.


I want this to be affordable and fairly simple.
Most of the players I talk to really like the cathode biasing but with respect to many of the harp amps I've made... some have both cathode and fixed bias.
I think the hard Chicago boogie players like the colder fixed bias tone.
I'm thinking of trying "cold" cathode bias with the zener diode mod talked about in the other threads.

I have tens of thousands of vintage carbon comp resistors and boxes and boxes of 200v to 630v Paper in Oil caps, from 680pF to .33uF.... I'd like to use some of them too.
The PT I'll use (that fits this smaller chassis) is 680CTvac@160ma.
The OT will be my custom wound tweed +30 watt 6L6 OT.
Any tweed Deluxe iron fits too so I can make a 10w, 18w, 30 watt version with combination's of power tubes, trannys and rectifier tubes.

I really want to use up the last of the "5F11" tweed cabinets.
These are all made with the 12" baffle board though. They are almost the same size as a 5E3 narrow panel tweed Deluxe, but the 5F11 does not use the same size chassis... 5F11 is a bigger chassis. Hence th reason I can get Vol, Treble, Bass and Line Out on the top face.
I do have a couple spare 1x10" baffles that would fit, but I don't think I want to try anything smaller then the 12" in there right now and there is no way two 10"s would fit right.
However, the next step will also be a larger tweed 2x10 Super sized cabinet (since I have more then a half dozen of those 5F4 cabs left too)... then I could make it up with the std 2x10s or a new 12" and 8" combo which I really like too.
No sure if I could get a 10 and 12 in there.

Speakers:
We've been messing with a few speakers here and found that the generic Eminence hemp coned Cannabis Rex 12" actually sounds pretty darn good... but only if the actual preamp is tuned a ways down from the 3Khz to 4Khz spikiness of that speaker and not with a tone control.
That speaker is just a bit heavy for what I'd like to do in a 3/8" baffle board though.
The other option is a custom made 12A125/P12Q from Weber with a smooth cone. I did not like the 12A100 at all.
I'm not a big fan of those nor the Signature series but others like them a lot.

Please, keep those suggestions coming.

[ThermionicScott]

I don't know many harp players personally, butd oes the desire for simplicity outweigh the flexibility you could get through a couple switches?

As an engineer, it seems like you could cover a lot of ground using a fixed/cathode-bias/cathode-bias-without-capacitor switch, as well as a switch for tube/SS rectifier. Ditto for a TMB+Presence tone circuit.

Since each harp player seems to want different characteristics, I think it would be well nigh impossible to design one amp that would satisfy a large number of them.

- Scott

P.S. Anyone tried pairing a 15" speaker with an 8" or 10"? In theory, it seems like it could combine good thump and body with attack, but perhaps there's a reason you don't see much of that combo. (Hey, how about wiring one of those resistive attenuator circuits in with the smaller speaker to "dial it out"?)

[MWJB]

"as well as a switch for tube/SS rectifier" Could do, but most guys in a gig situation can't really tell if they have a SS rectifier or not, as long as the amp sounds good with SS that is...subbing a tube for the Sovtek SSR is quick & simple enough. In cathode bias especially, a SS rectifier might not be misssed at all (again, assuming amp is designed with SS in mind).

I haven't heard any amps with a 15" for harp, that really have good "thump & body", tend more towards, brassy, middy, hornlike tones...it's big cone for a harp signal to move...probably best to keep it on it's own.

[Bruce / Mission Amps]

I believe you're on the right track Bruce. 5E5 is a nice circuit.
Mixed speaker sizes give the best of two worlds. If you not have enough room for 1x12 speaker in combination with 1x10 you can try 1x10 and 1x8.
i dont think i can recommend one size of speaker cause one amp works fantastic with a 12 and another is better with 2x8 or 2x10. It depends on how efficient the speaker is and how much you have to turn the amp up before it begin to breakup in the preamp.

Well, Rick (Davis) who has been giving me some input too, also wants me to try a 12" and 8" combo in the 5F4 cabinet as soon as I get the chassis up and running.
I'm pretty sure Gary's (Sonny Jr) Cruncher is another tweed 4x10 Bassman, made by MOJO musical supply for him and I really don't want to do just another harp tuned tweed Bassman.
The 3x10 tweed Bandmaster format might be interesting but it is only a little smaller then the Bassman...
Al Chesis uses one that I made for him... I do a lot of amp refurbing and tweaking for Al

http://www.deltasonics.net/fr_index.cfm

I have a 30 watt 5F4 amp with two Weber P10Rs in it, tuned for harp.
I sent that one down to the Handy Awards a couple years ago for a back line amp.
It got used a lot and was fairly well received. Unfortunately, it ended up going out on tour with a couple other players I barely even knew and not coming home for about 8 months! sheesh. It is well used now.

But, what about the actual speakers...
Some players like the Alnico way better then ceramic but I think the only
three makers of Alnico speakers are SICA (reissue Jensen), WeberVST and Eminence. I don't know if I like very many of those.
I've modded a few old brown face Concerts for harp and they sound killer with two ceramics and two Alnico speakers... same thing with a 3x10 tweed Bandmaster.
BF 4x10 Supers do not sound as good though.

[Bruce / Mission Amps]

I believe you're on the right track Bruce. 5E5 is a nice circuit.
Mixed speaker sizes give the best of two worlds. If you not have enough room for 1x12 speaker in combination with 1x10 you can try 1x10 and 1x8.
i dont think i can recommend one size of speaker cause one amp works fantastic with a 12 and another is better with 2x8 or 2x10. It depends on how efficient the speaker is and how much you have to turn the amp up before it begin to breakup in the preamp.

Yeah, I could get a DPDT switch in the bottom for fixed or cathode power tube biasing.

[arnenym]

Well, Rick (Davis) who has been giving me some input too, also wants me to try a 12" and 8" combo in the 5F4 cabinet as soon as I get the chassis up and running.
I'm pretty sure Gary's (Sonny Jr) Cruncher is another tweed 4x10 Bassman, made by MOJO musical supply for him and I really don't want to do just another harp tuned tweed Bassman.
The 3x10 tweed Bandmaster format might be interesting but it is only a little smaller then the Bassman...
Al Chesis uses one that I made for him... I do a lot of amp refurbing and tweaking for Al

Delta Sonics - index

I have a 30 watt 5F4 amp with two Weber P10Rs in it, tuned for harp.
I sent that one down to the Handy Awards a couple years ago for a back line amp.
It got used a lot and was fairly well received. Unfortunately, it ended up going out on tour with a couple other players I barely even knew and not coming home for about 8 months! sheesh. It is well used now.

But, what about the actual speakers...
Some players like the Alnico way better then ceramic but I think the only
three makers of Alnico speakers are SICA (reissue Jensen), WeberVST and Eminence. I don't know if I like very many of those.
I've modded a few old brown face Concerts for harp and they sound killer with two ceramics and two Alnico speakers... same thing with a 3x10 tweed Bandmaster.
BF 4x10 Supers do not sound as good though.

I modded a old PA head to a friend and he wanted a threeknob tone control. I found a very good circuit-mix of 5F4 and 5F6. It sound gorgeous.
Its a bassman style preamp with bass, middle and treble control and a cathodyne PI and a cathode biased 2 X 6L6 final.

[MWJB]

"I'm pretty sure Gary's (Sonny Jr) Cruncher is another tweed 4x10 Bassman, made by MOJO musical supply for him and I really don't want to do just another harp tuned tweed Bassman." Gary makes a 4x10, but the Cruncher is (1x12" + 2x8"), with the 5F6A circuit, built by Keith Robb (his own layout) AFAIK at present.

"Some players like the Alnico way better then ceramic but I think the only
three makers of Alnico speakers are SICA (reissue Jensen), WeberVST and Eminence."...and Fane, but I'd only use 1, or 2 tops for punch. Otherwise, every player I know who has A/B'd the SICA (crap in a tweed, too scooped in the mids, no body, not so bad in a tolex amp though)/Weber/Emi has preferred the Emi, fuller, meatier tone with a less clanky, metallic character than the others...Kinder used them & many harp players looking for an RI opt for the older version equipped with the Emis. No real preference between the blue (25W) or the black (35W).

In a 3 or 4x10" I too like a mix between a couple of Emis for character & 1 or 2 smoother, darker, punchier ceramics to round out the sound. Gary O uses the Emi 105, not my favourite (middy, bitey, shelves the low end a bit early).

3x10" Tweed Bandmaster - would you keep the choke input filter? I'd be tempted to place the choke between the screens & main B+ like on later amps.

Kendrick built a (1x10" + 1x12") amp based on the 5E# circuit.

[Bruce / Mission Amps]

"I'm pretty sure Gary's (Sonny Jr) Cruncher is another tweed 4x10 Bassman, made by MOJO musical supply for him and I really don't want to do just another harp tuned tweed Bassman." Gary makes a 4x10, but the Cruncher is (1x12" + 2x8"), with the 5F6A circuit, built by Keith Robb (his own layout) AFAIK at present.

"Some players like the Alnico way better then ceramic but I think the only
three makers of Alnico speakers are SICA (reissue Jensen), WeberVST and Eminence."...and Fane, but I'd only use 1, or 2 tops for punch. Otherwise, every player I know who has A/B'd the SICA (crap in a tweed, too scooped in the mids, no body, not so bad in a tolex amp though)/Weber/Emi has preferred the Emi, fuller, meatier tone with a less clanky, metallic character than the others...Kinder used them & many harp players looking for an RI opt for the older version equipped with the Emis. No real preference between the blue (25W) or the black (35W).

In a 3 or 4x10" I too like a mix between a couple of Emis for character & 1 or 2 smoother, darker, punchier ceramics to round out the sound. Gary O uses the Emi 105, not my favourite (middy, bitey, shelves the low end a bit early).

3x10" Tweed Bandmaster - would you keep the choke input filter? I'd be tempted to place the choke between the screens & main B+ like on later amps.

Kendrick built a (1x10" + 1x12") amp based on the 5E# circuit.

I like the B+ rail but it's not actually a choke input filter... it's a brute force PI filter.
What I don't like about it (and I change it) is that the screen voltage node is take from the center tap of the OT.
I use a 2k7 2 W resistor there with another node cap.