This is out of a Hammond H-100. The bass signal is "derived" by combining the left and right channels, then filtering for the bass section. The tubes are new, the DC output on the recto tubes does not dive under load, all electro caps have been replaced, the speaker is good, and it sounds good, except the lower end seems weak in terms of power.
Is there anything to be checked, or some modification be made that won't ruin anything?
Thanks.
Is there anything to be checked, or some modification be made that won't ruin anything?
Thanks.
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Should be good for up to 40Watts. The bass response is down to the amount of iron in the output transformer and the speaker/cabinet type.
Just a thought, I had a Fender Twin Reverb, 1965 model with poor bass response, that was shorted turns in the output transformer, causing lack of flux and poor bass response.
Just a thought, I had a Fender Twin Reverb, 1965 model with poor bass response, that was shorted turns in the output transformer, causing lack of flux and poor bass response.
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4 Ohm resistive load: 40V 1.6A
4 Ohm Speaker: 60V 1.5A
I increased the input signal significantly with no effect. I can do this easily since I replaced all the preamps with opamps. It's as if there is a limiter in there.
Thank you for the prudent idea.
According to the manual, total power for L, R, and Bass is 60W E.I.A. (The EIA rating, established by The Electronic Industries Association, reflects the power output for a single channel driven at mid-band – typically 1 kHz – with 1% THD clipping. This standard inflates the amplifier’s power points to 10 to 20% higher than the FTC ratings.)
Perhaps I'm expecting too much. There is no cabinet--it's open air. The output transformer is 50 years old, and there's no data given for resistance for my particular model. The diagram indicates an 8 Ohm speaker--mine has a 4 Ohm. In fact, I have been unable to locate the correct diagram for my unit, except that I know it' the last of the Mahicans.
I have the big bottle 7591s, so perhaps an OT with different characteristics could boost the output without smoking something. Incidentally, I did zero out the balance pot so there was no DC on the OT input. It was not off much at all.
Thank you for your ideas.
I will check it again. I'm working with a $30 Radio Shack DMM that's 15 years old, and perhaps I messed up the connections.Hi,
There is something wrong somewhere !
40V across a 4 Ohm resistor should produce a current of 10A and a power of 400W.
How hot is the resistor ?
I just replaced the speaker with a 4 Ohm, 20W ceramic and ran max output for 30 seconds. I got warm but 10A would have been untouchable.
It seems that perhaps nothing is wrong.
I'm no valve amp.expert but I recall reading that using a 4 Ohm load on 8 Ohm tap will shift the high pass frequency up (DC blocking and infra sound filter). I guess it follows that the high end roll off would be altered too.
That may account for your impression that bass is lacking.
If possible I would suggest using one speaker for an 8 Ohm load.
And also I would lower your expectations regarding bass output very significantly, IF the cab is open back.
That may account for your impression that bass is lacking.
If possible I would suggest using one speaker for an 8 Ohm load.
And also I would lower your expectations regarding bass output very significantly, IF the cab is open back.
Good thought. The unit was built when everyone knew they were going down the pipe. There is no reason not to suspect they just threw in the 4 Ohm either due to supplier problems or to correct some user dissatisfaction.
An 8 Ohm speaker I suspect would have less of an overall SPL when compared to a 4 Ohm on the same system?
Interestingly, the two smaller 8 in. L and R speakers bleed some bass. I suspected an out-of-phase condition was attenuating to some degree, but disconnecting them made no difference.
An 8 Ohm speaker I suspect would have less of an overall SPL when compared to a 4 Ohm on the same system?
Interestingly, the two smaller 8 in. L and R speakers bleed some bass. I suspected an out-of-phase condition was attenuating to some degree, but disconnecting them made no difference.
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Speaking of the cabinet, the unit did come with a back from the factory (which is missing), but it was particle board with many slots for airflow so the electronics near the top would not melt.
Looking at some of the recommended bass reflex cabinet sized and ports, even the stock back may have had some boosting effect.
The unit is good for recording or playing in a small room. I'll leave it that for now. Maybe try an 8 Ohm at some point. I will also check for way out ohm readings on the OT, and swap the driver tube.
Thank you for your opinion.
Agreed. It looks like there is nothing wrong with it. If I do manage to boost output, the speaker may bottom out in the ends of its excursion.
Thanks for that reminder.
No baffle at ALL? Even a Fifteen-Inch is gutless all by itself.
Or do you mean the typical open-back cabinet of the day? Even a 2 foot wide baffle *considerably* helps; a 30" face with 20" sides can deliver heavy bass. Even though not sealed.
Well, the H100 is designed for an 8 ohm speaker. My Original H100 organ with new ecaps will rattle the chandilier in a 14'x20' room. Gutsy bass was a particular sales point of the model. Rohm or something drivers? They were designed to be backed into a hard wall, about afoot away, IMHO. With or without baffle.
Mine puts out real 40 W on the speaker, ie about 17 v. Be sure to use an ANALOG VOM to read AC voltage, or a scope. I've gotten quite random AC results with Craftsman DVM at music frequencies. DVM are fine at 60 hz, which is between bflat1 and b1 on the 16' drawbar.
Pity another one bit the dust. Killed by all the e-caps, I'm the only guy in the world that replaced 77 of them in one unit. With tired e-caps H100 sound like a wet kazoo.
Mine puts out real 40 W on the speaker, ie about 17 v. Be sure to use an ANALOG VOM to read AC voltage, or a scope. I've gotten quite random AC results with Craftsman DVM at music frequencies. DVM are fine at 60 hz, which is between bflat1 and b1 on the 16' drawbar.
Pity another one bit the dust. Killed by all the e-caps, I'm the only guy in the world that replaced 77 of them in one unit. With tired e-caps H100 sound like a wet kazoo.
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No. I decided to simplify it closer to a B3. All those wires and switches were too much to deal with, not to mention all those Harp caps. I did leave the reverb, however. But I do not use banjo or marimba, etc. The Celeste was interesting but nothing like a Leslie. Even with all the superuflous removed, there are still a host of bad connection and dirty switch contacts.
I also added an RCA loop and experimented with "Shimmer" reverb. Works good until chords or notes are played around middle-C with the higher frequencies pulled out. The signal skyrockets and makes the shim-verb crackle. I could play all the up to the top but with only the first 4 drawbars out all the way. Interestingly, the "Harp" feature was limited to the first two octaves or so, I assume for the same reason. There is some "bleed" from adjacent frequencies in the tone generator, which may be causing it. In any case, Hammond could not overcome the problem.
Oh, good a real organ. B3 is a good goal, but getting the perc function to even work is a challange in the 50th year. My gloc and xyl are quite interesting after all the caps were changed. You can relocate some wires on banjo to make a threes overtone like the B3. The tab switches are all palladium plated, mine responded fine to spraying them out with contact cleaner. My units are early however. Later (post ser 15000?) units had grease on the tab contacts that dried out, those the tab switches have to be disassembled and paste/dirt scraped/washed off to make them work. Same problem on drawbar contacts on late units, mine don't drop out, Bob's late ones did.
Reverb was dead on ser 9574 with the series e-cap bad, another ser 1122 had the reverb cap replaced in the 80's and worked just fine. There is some bass cut on reverb, for a purpose. reverb on H100 is 7 vac out 25 mvac in so it is not really compatible with 2 v digital sustain units. Putting a transistor circuit in instead of the tubes should do the trick. The wiring on reverb is superb, no hum although they run 10'.
Harp is really a sustain, 1122 had all 112 harp ecaps replaced in the 80's, and I don't like it, it smears too much. 9574 has about the right time constant of susteain but the caps are inconsistent, I need to replace them with some consistant value so all notes are the same. Bleed in the tone generator is not typical, my units don't do it. I do have some high tones running continuously from the bad trigger harp e-caps in 9574, another reason to figure out which ones are trigger (that causes tone bleed) and which ones are sustain time.
BTW is got over enthusiastic on watts in post 15. I think 7591bass channel is 30 W, each 6BQ5 output is 7 watts for about 44 W total. My bass puts out the voltage appropriate for 30W.
A slotted back might help bass but change the 15" driver to 8 ohms first. and A Peavey black widow maybe?
Coupler e-caps in the power amp usually are bad, the bass boost cathode bypass e-cap is tantalum and always bad, The 10K 1W voltage drop resistors in the power amp have all been 11.5k, and look burned, so change those to a 2 W at least 10k unit to get maximum B+ to the power tubes. The 220 ohm B+ drop resistor was burned and high value in #1122.
Reverb was dead on ser 9574 with the series e-cap bad, another ser 1122 had the reverb cap replaced in the 80's and worked just fine. There is some bass cut on reverb, for a purpose. reverb on H100 is 7 vac out 25 mvac in so it is not really compatible with 2 v digital sustain units. Putting a transistor circuit in instead of the tubes should do the trick. The wiring on reverb is superb, no hum although they run 10'.
Harp is really a sustain, 1122 had all 112 harp ecaps replaced in the 80's, and I don't like it, it smears too much. 9574 has about the right time constant of susteain but the caps are inconsistent, I need to replace them with some consistant value so all notes are the same. Bleed in the tone generator is not typical, my units don't do it. I do have some high tones running continuously from the bad trigger harp e-caps in 9574, another reason to figure out which ones are trigger (that causes tone bleed) and which ones are sustain time.
BTW is got over enthusiastic on watts in post 15. I think 7591bass channel is 30 W, each 6BQ5 output is 7 watts for about 44 W total. My bass puts out the voltage appropriate for 30W.
A slotted back might help bass but change the 15" driver to 8 ohms first. and A Peavey black widow maybe?
Coupler e-caps in the power amp usually are bad, the bass boost cathode bypass e-cap is tantalum and always bad, The 10K 1W voltage drop resistors in the power amp have all been 11.5k, and look burned, so change those to a 2 W at least 10k unit to get maximum B+ to the power tubes. The 220 ohm B+ drop resistor was burned and high value in #1122.
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All the resistors were checked and all electros were replaced. I thought those two brown ones were Mylar, but now I see the polarity marks. They are the only tants left in the unit. They are 0.1uF (100nF) 400V.
Looks like the DMM is fried. Ohms won't zero out and it won't read a good AAA battery. This probably explains the impossible readings obtained above.
Thanks for your comments.
Another bass loss area, the electrolytic coupler caps in the preamp units on the back of the keyboard. I didn't take the boards off, I just cut the old leads, bent hooks in them, and hooked the new caps to the old leads. That wirewrap requires a 26 ga tool you can't buy to remove & replace.
Does your unit have a tube perc unit on the back of the keyboard, or a later transistor one? The transistor ones go totally dead as the little silver tantalum caps with the red ends shorted out decades ago.
The tube ones just get useless, as the power supply caps wore out, the big can.
BTW the silver coax core wirewraps on the preamps are 25 mvac signals, and tend to drop out from oxidation. Several of the ones on serial 1122 were soldered by dealer service, which solves the problem permanently. The orange and green wirewraps are 25 v & 100 VDC, not an oxidation problem.
There are various "sounds" of B3 depending on how deteriorated the wax/paper caps were when the recording was made. Some people like the duller sound of a 20 year old B3 with 25% low paper caps, some like the bright shiny sound of a B3 with mylar caps. The H100 has mylar caps. Keyboardpartners.de has a schematic marked up with suggestions of changes to make on the preamps to dull down the brightness of the H100 if you like that sound without the highs.
Does your unit have a tube perc unit on the back of the keyboard, or a later transistor one? The transistor ones go totally dead as the little silver tantalum caps with the red ends shorted out decades ago.
The tube ones just get useless, as the power supply caps wore out, the big can.
BTW the silver coax core wirewraps on the preamps are 25 mvac signals, and tend to drop out from oxidation. Several of the ones on serial 1122 were soldered by dealer service, which solves the problem permanently. The orange and green wirewraps are 25 v & 100 VDC, not an oxidation problem.
There are various "sounds" of B3 depending on how deteriorated the wax/paper caps were when the recording was made. Some people like the duller sound of a 20 year old B3 with 25% low paper caps, some like the bright shiny sound of a B3 with mylar caps. The H100 has mylar caps. Keyboardpartners.de has a schematic marked up with suggestions of changes to make on the preamps to dull down the brightness of the H100 if you like that sound without the highs.
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